I just installed MT 5.03. I have set it up to use PostgresSQL 9.0. Everything went well through the setup wizard and I logged in. I saw the dashboard and then clicked on a link to the first blog I had setup and got this error:
"Can't use string ("x42494e3a53455247000000000000000") as an ARRAY ref while "strict refs" in use"
And now I can return to the my /mt URL, click on "Sign in to Movable Type", and the login form displays. If I enter an incorrect login/password combo it tells me my login is invalid. If I enter my correct login/password I get the same error as above.
The only other odd thing about my setup is that I'm running it under Tomcat 7.0.2. CGI and everything seems to be working properly.
I just did a dump of my movabletype database and found where this string occurs. It is in the mt_author_meta table, column author_meta_vblob. In Postgres this is a data type of bytea. Is this some incompatibility between MT5 and Postgres, or is there some kind of workaround available?
Each click within the dashboard presents me with the login form telling me that my session has expired. If I then delete everything from author_meta_vblob i can login and it takes me to the page I had tried to load previously.
Any help would be greatly appreciated.
Reported on Movable Type 5

IIRC, Postgre is no longer officially supported. It's sort of "you're on your own" now. Apparently, only a handful of users were using it and SixApart decided their resources were better spent on other areas.
Yup, Postgres is no longer officially supported. I was hoping that someone here would still be using it with MT5 and might be able to offer some help.
You can always get on the MTOS mailing list and see if anyone can help you there. Jun and other MT developers participate and might be able to help you.
Would the mtos-dev list be the correct place for that?
Yep
From the mailing list I was pointed to a Japanese site that had the fix.
Edit your postgresql.conf file and set:
bytea = 'escape'
Then run:
pg_ctl reload
And now Postgres 9.0 is working with MT5.