Ordinary User Can't Login "Site Suspended"

Greetings,

I have a big problem here and I think this is the perfect place to ask this question.

We run BP and WPMU plugins, I received complains from our Subscribers that they can't login because there is this "Site Suspended".

I need your help or advice on how to fix this ASAP because my email is full complain now..:disappointed:

TIA
Patrick