Have you tried playing around with the video settings in the preferences? Changing the codec to microsoft 1, change the quality settings, framerate? I don't know too much about the va12 but the va11 seemed to do the same thing until..... I found blue iris security software.
It seems to me that the va11 or even maybe the va12 isn't the problem it's AHP Iwitness plugin. I switched to Blue Iris and everything is running alot more smoothly. Not saying it will work with your situation, but it is worth a try. You can find it here:
http://blueirissoftware.com/index.html They have a 15 day trial and also have two options of buying, a one video input (which is okay for using the va11 or va12) or the unlimited video source. Both are under $50.00 .
There is a third party program for it called bicommand that is a commandline tool to start recording, stop recording, triggering and etc... That way you can use the macros in AHP to start a batch file or autohotkey script from the run windows command when a motion sensor is tripped to start the recording, delay 1 min and stop the recording.
Before using Blue Iris I was using AHP, BVC, PCC and my system would barely run! BVC would stutter, commands were lost or would wait for 5 minutes before firing.
My suggestion is to play with the preferences in AHP first and then maybe try the Blue Iris software. It is well worth the money, hasn't crashed yet either. And you can use any kind of camera or video input you want... IP cameras, x10 cameras, personal webcams, any kind of capture device, anything!
Just make sure you start Blue Iris before you start AHP so AHP doesn't steel the va12 from you.