Mikusek the requirements should be met - the forum name should contain lowercase alphanumeric characters with no spaces. The conversion to lowercase should be done automatically, which makes me think that the verification fails elsewhere (maybe there is an invisible whitespace character surrounding the string somehow, or the JavaScript acts up - do you have turned it on in your browser?). Either way or not, I will have a look into this and fix the form filter (currently, it seems to work for me with the name you chose).
If you want, you can e-mail me the tag and I’ll register it for you (with your email address) until I fix the form.
