In the frontend, an error message is displayed saying that the class 'GeSHi' would already be declared. The mm_forum extension includes the Generic Syntax Highlighter class (GeSHi), therefore some problems might occur in connection to other extensions that use GeSHi. However, this is not a problem of the mm_forum extension, since in the mm_forum extension, the GeSHi class in only included if it did not exist until the time of inclusion. On the other hand it cannot be guaranteed that other extensions check this before including the GeSHi class.

Users that were imported from a phpBB forum cannot log in!If you import user data from a phpBB message board, you should install the extension kb_md5fepw. The reason for this it that in the phpBB board, user passwords are stored only as encrypted MD5 hash, while the regular TYPO3 authentication method uses clear text passwords. Since the MD5 algorithm is a one-way encryption, there is no (easy) way to retrieve the clear text passwords from the MD5 hashes. The kb_md5fepw extension changes the TYPO3 authentication method to work with MD5 encrypted passwords.

Some forms can not be submitted when the server OS is a Windows system!  This is related to how Windows handles URLs. Windows uses backslashes (\) in URLs which occasionally leads to 'hiccups' in the forum system. A workaround for this problem should be to either use the config.baseURL variable or to switch to Linux. Just joking.