If you're using a slightly older version of Wifi Tethering then that would be the problem. I used to have all kinds of trouble with it until the version that supports WEP came out. If you have kept your data when switching between ROMs that might be the problem. You might want to try a full wipe and then use the Wifi Tether that AdamZ posted here:
http://alldroid.org/download/file.php?id=1563