Modifying themes/css logs me out?

[jkrlvgn]

I've been brought in to help with a forum of a friend of mine.  It's pretty heavily modded, but there weren't any real issues until after they decided to move hosts.  I could swear it was a permission issue, but everything -looks- right...

No matter what file in the modify theme area, be it CSS or template files, once someone clicks on "save", it logs that person out and shows the default theme...but not really!  Because you can go back to the forum anywhere else, and it has that person logged in fine.

I'll be happy to get a list of the mods, if I need to, and I tried to look through Searches here (and found multiple things that were CLOSE), but none of the situations seemed to help.  I've tried the fix_settings tool, even, and it seems to do nothing.  Changed cookie names, changed settings in the server settings in the admin menu...

Help?

[Illori]

ask your host if they have mod_security enabled, if so ask them to disable it.

[jkrlvgn]

I hate everything about you.  *LOL*  Of course, that was it.  I asked her if it was on, she said no.  Luckily, it has the option to turn it off in her cpanel.  Her previous host must have turned it off, and she...forgot.

I'm sorry to have wasted your time..!  Thanks a lot.