You need to post in the modification area, because we have no idea what "MOD" you are referring to. The problem you are having is related to the modification in some way. How are the volunteers on vbulletin.org going to be able to assist you if you do not listen to our initial advice? If you want free assistance you need to work with the people delivering it.
At this point the only thing I can recommend given the absolute lack of data you have given us is to check your logs.
Sorry, about being so blunt. It is really not my nature, but I am using the 2x4 approach.
For official support open a ticket at vbulletin.com. However, they do not answer questions about modifications. Modifications are not vBulletin Products and are not part of your license agreement.