This forum really isn't that compatible with Sun One ASP, they have changed some things in recent versions that cause problems with the forum. If you do a search for Sun One in this forum, you should find some recent topics on the changes necessary to get the forum somewhat working.
You should't by any chance use B-One as host?? I have had a forum running for 3-4 weeks as well. And today i received the exactly same error but first in the file inc_func_common.asp...but right now it says it is in the default.asp..but in line 160 though.....
You just need to tell them that the forum no longer works and no code was changed. That means there is something wrong with the server and they should fix it. If they don't help you with your problem then... well I guess I would know what to do.