The limit is hard-coded into the BBS I believe.

I think the problem isn't the size of the limit, part of it is that the text telling the user about it isn't easily readable. It should say "100k" instead of "100000 bytes".

Also, one of its major problems is that should give them an error message and allow them to re-upload if they exceed the limit. The fact that people can post and think it's OK because they're not prompted for a re-try is really the root of the problem.