You should be able to use whatever characters you need for forum and category descriptions. The only place that you can't use special characters is for the keywords when creating a board. It's not something I can fix because of the way the form fields and the sql queries work, but I'll need to put in more checking for the use of special characters.
If you didn't use any special characters for the keywords then there must be a different problem. Need to elimate the first in order to figure out if it is something else.
