Samplitude pro X5. Win 7 64 bit. Plenty of ram. Motu 24I.

Samplitude was working fine, then it crashed the computer a few times. Now it works, but throws an error and dies when I try to use an external keyboard with a soft-synth. When I press a key, a get a brief audio blip (as if it were trying to sound the note). Then, it dies and the error box says "The instruction at 0x40z1ee99 referenced memory at 0x0000000c. The memory could not be Read." Then the program closes. The error message is always the same.

By trial and error I have determined that the problem is in samplitude:

1) The external keyboard works fine with soft-synths outside of samplitude.

2) When I try a different keyboard and a different USB port (in samplitude), the error persists.

3) It doesn't matter which soft-synth I use; I get the same error (as long as I am within samplitude).

4) With the monitoring and recording button deactivated, I can press keys on the keyboard without errors. I can get audio from the soft-synths without problems if I don't use the external keyboard (i.e. use a virtual keyboard built into the soft-synth). It is only when turning on monitoring or recording and subsequently pressing a key on the keyboard, that it dies.

I am baffled. Any clues? Much appreciated.