Fatal error issue...help?

[Moxi]

Tonight when I went to check some permissions for one of my usergroups in my admincp, I couldn't access any of my usergroup settings or the "add new usergroup" sections, when I tried to do so it returned this error:
Fatal error: Cannot use string offset as an array in /home/sskies/public_html/includes/class_bitfield_builder.php on line 312

I'm not even sure what this even means?

I was able to access everything else in my admincp without problem (except the administrator permissions area, which returned the same error), but I haven't changed anything anytime recently, and I know it was working a few weeks ago. I have no idea what might be causing the problem. Does anyone have any idea what might be causing the problem or what I can do to fix it?

I'm using version 3.5.0 and I have a number of mods installed, but again, it was working fine recently and I haven't changed any files or templates or anything at all in months probably, short of adding a couple new usergroups. I think my host might have recently upgraded from php4 to php5, might this have anything to do with it?

Any help would be greatly appreciated
Thanks in advance!