Since the page blanks out AND others don't seem to have this issue, the only way for me to say anything sensible about it would be to see your Apache error log entries that probably show up when trying to post a comment. I wouldn't know how to look into this otherwise because I cannot reproduce the problem myself. Nor on my hosting provider nor on my local box.
Thanks, since it works for other templates i don't know what went wrong but i restored the original function_comment file and it works fine now. Thanks again for this great template.