I have started getting this error
Writing to '/home/notsvill/public_html/atom.xml.new' failed: Opening local file '/home/notsvill/public_html/atom.xml.new' failed: Permission denied
Any clus what could be the cause of this. I have upgraded to 5.1, but it was working fine after the upgrade. This just "developed."
- jack lail
Reported on Movable Type 5

Have you checked if the permissions/ownership of the folder where you are publishing your blog is still the same? The webserver user (and if you are running the run-periodic-tasks script, the user that is running this script) needs to have permission to write there.
Turned out a cpanel upgrade had hosted some things on my host for a bit and that was just the time I was uploaded files. They had no owner. They fixed that and all is well. Turned out not really be a MT issue at all. Thanks for your response!