My cp is at http://www.clanbeowulf.org/clanbeowulfcgi/cp.cgi (doesn't work).
I had the latest v5 (v5.47e?) running fine then decided to upgrade. I thought I followed very strictly. When I was done, I was able to log into my CP and I was pretty sure I did everything in order. Everything came back "OK". However, when I was done the forum ultimatebb.cgi wouldn't come up. (Internal Server Error).

I went back and redid everything.... same. Then I tried getting back into v5... no go.
Now, ubb6_test says everything is "OK" except the paths are now not working. Also, the CP doesn't come up anymore (500ISE). Hello's are fine.

Next step gurus?

what version are you using because the problem for me was fixed by checking all permissions, paths, making sure all files that are uploaded in ascii are uploaded in ascii and lastly,
doing this

2) Open ubb_lib.cgi in a text editor(notepad will work).
3) Look for line 15 $masterCharset = '';
4) Adjust the charset to your proper charset. For most boards in English the charset would be ISO-8859-1 so the line would read
$masterCharset = 'ISO-8859-1';
5) Lastly reupload all cgi-bin files but not variable files!

It looks like v6.3 fixes that little error. It looks like it sets Mastercharset unless already set with something else.

However, I did reupload variables to try and get things working before I posted here.