PLEASE HELP ! Software Instruments not responding to MIDI input - Mainstage 2.1.3

I am running Mainstage 2.1.3 on my Intel MacBook Pro with OSX 10.6.8 4gb ram

Everything was working fine - until the last update to 2.1.3 about a year ago. 😢

I wasn't using MS much at the time and I figured there would be a fix in the meantime...

????????????

But now the problems I am having are...

A) All my software instruments have stopped responding to MIDI input

B) sometimes MS crashes (most important because I want to use it live)

So this app is worthless to me now...😠

I DO NOT want to upgrade to OSX 10.7 because EVERYTHING ELSE that I use WORKS (including Logic 9)

Maybe I could REVERT to an older version of Mainstage ? If this would fix it I would do it in a heartbeat but I would need someones' help....

I know it's asking for a miracle but can somebody PLEASE, PLEASE help me? I have a very important gig coming up next weekend

Thanking all in advance!

Tunapianaman