Oh yeah, and I have verified the files were uploaded correctly and that all the permissions are set as they should be as well.

I had the same issue on a test site. I figured out that the problem was related to the /cgi-bin/mt directory permissions being changed to 777.

I had checked all the other files, re-uploaded, etc. Missed that simple thing.

I've checked permissions on all folders and they're all correct too. Still no luck with logging in. I am able to enter my username and password, but when I click "sign in" I get the 500 Internal Server Error.

Any other suggestions anyone?

Does mt-check run correctly?

Yes it does. http://neocarla.com/cgi-bin/mt-check.cgi

Anything else in the web server logs?

Here's the log:

[2008-07-26 02:31:16]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-26 02:31:05]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-26 02:30:33]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:57:16]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:57:16]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:57:13]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:57:11]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:56:31]: error: file is writable by others: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:51:56]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:51:55]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:51:55]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:51:49]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:51:45]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:51:35]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:51:19]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-25 22:04:41]: error: directory is writable by others: (/home/neocarla/publichtml/cgi-bin) [2008-07-25 22:04:33]: error: directory is writable by others: (/home/neocarla/publichtml/cgi-bin) [2008-07-24 17:07:32]: error: file has no execute permission: (/home/neocarla/publichtml/cgi-bin/mt/mt.cgi) [2008-07-24 13:50:25]: error: directory is writable by others: (/home/neocarla/publichtml/cgi-bin) [2008-07-24 13:50:17]: error: directory is writable by others: (/home/neocarla/publichtml/cgi-bin) [2008-07-24 02:08:05]: error: file is writable by others: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [2008-07-24 02:07:54]: error: file is writable by others: (/home/neocarla/publichtml/cgi-bin/mt.cgi) [Sat Jul 26 16:19:57 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/500.shtml [Sat Jul 26 16:19:57 2008] [error] [client 66.137.224.189] Premature end of script headers: /home/neocarla/publichtml/cgi-bin/mt.cgi [Sat Jul 26 16:15:44 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/500.shtml [Sat Jul 26 16:15:44 2008] [error] [client 66.137.224.189] Premature end of script headers: /home/neocarla/publichtml/cgi-bin/mt.cgi [Sat Jul 26 16:15:35 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 16:15:35 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/favicon.ico [Sat Jul 26 16:15:35 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/500.shtml [Sat Jul 26 16:15:35 2008] [error] [client 66.137.224.189] Premature end of script headers: /home/neocarla/publichtml/cgi-bin/mt.cgi [Sat Jul 26 16:00:10 2008] [error] [client 74.6.17.160] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 16:00:10 2008] [error] [client 74.6.17.160] File does not exist: /home/neocarla/publichtml/mt/entertainment/ [Sat Jul 26 16:00:10 2008] [error] [client 74.6.17.160] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 16:00:10 2008] [error] [client 74.6.17.160] File does not exist: /home/neocarla/publichtml/robots.txt [Sat Jul 26 15:55:30 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/500.shtml [Sat Jul 26 15:55:30 2008] [error] [client 66.137.224.189] Premature end of script headers: /home/neocarla/publichtml/cgi-bin/mt.cgi [Sat Jul 26 15:53:27 2008] [error] [client 66.231.189.93] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 15:53:27 2008] [error] [client 66.231.189.93] File does not exist: /home/neocarla/publichtml/mt/fyi/ [Sat Jul 26 15:53:26 2008] [error] [client 66.231.188.51] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 15:53:26 2008] [error] [client 66.231.188.51] File does not exist: /home/neocarla/publichtml/robots.txt [Sat Jul 26 15:53:02 2008] [error] [client 86.130.228.149] File does not exist: /home/neocarla/publichtml/500.shtml [Sat Jul 26 15:53:02 2008] [error] [client 86.130.228.149] Premature end of script headers: /home/neocarla/publichtml/cgi-bin/mt-config.cgi [Sat Jul 26 15:52:32 2008] [error] [client 72.29.65.116] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 15:52:32 2008] [error] [client 72.29.65.116] script not found or unable to stat: /home/neocarla/publichtml/cgi-bin/mt.js [Sat Jul 26 15:48:03 2008] [error] [client 86.130.228.149] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 15:48:03 2008] [error] [client 86.130.228.149] File does not exist: /home/neocarla/publichtml/favicon.ico [Sat Jul 26 15:48:00 2008] [error] [client 86.130.228.149] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 15:48:00 2008] [error] [client 86.130.228.149] File does not exist: /home/neocarla/publichtml/favicon.ico [Sat Jul 26 15:21:31 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 15:21:31 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/favicon.ico [Sat Jul 26 15:21:28 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 15:21:28 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/favicon.ico [Sat Jul 26 12:18:52 2008] [error] [client 65.55.105.86] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 12:18:52 2008] [error] [client 65.55.105.86] File does not exist: /home/neocarla/publichtml/robots.txt [Sat Jul 26 10:21:26 2008] [error] [client 87.234.234.66] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 10:21:26 2008] [error] [client 87.234.234.66] script not found or unable to stat: /home/neocarla/publichtml/cgi-bin/mt [Sat Jul 26 10:21:22 2008] [error] [client 222.73.41.9] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 10:21:22 2008] [error] [client 222.73.41.9] script not found or unable to stat: /home/neocarla/publichtml/cgi-bin/mt [Sat Jul 26 09:50:33 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/404.shtml [Sat Jul 26 09:50:33 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/favicon.ico [Sat Jul 26 09:50:33 2008] [error] [client 66.137.224.189] File does not exist: /home/neocarla/publichtml/500.shtml [Sat Jul 26 09:50:33 2008] [error] [client 66.137.224.189] Premature end of script headers: /home/neocarla/publichtml/cgi-bin/mt.cgi

I just did a new install, and all seems to be fine thus far. And still not certain what was screwed up with the R3 to R4 upgrade.

Thanks to those of you who replied.