APC40 sometimes crashes/freeze

hello everybody,

live 8.1.1; MacPro Duo; OS X snowleo

I put some selfmade Samplerinstruments (with mapping on macros) on a track, APC40 work fine locked automatically lower 8 encoders on macropotis, now I put some effectracks behind like channelstripes or vst plugins using as inserts or as effektchannels.
After a while the APC40 lost the mapped lower 8 encoders. It´s impossible to turn the macroknobs via APC. Suddenly some effectparameters from the chain respond on encoders but not the macropotis. The LED cyrcle around the encoders stay dark. Sometimes the APC40 freeze completly. Sometimes I can push some buttons like "stop all clips". Sometimes it plays notes if I push buttoms after a crash.

I have to restart live. But if I save a arrangment with the crashed APC40. The problem (chrashed APC40) comes from the beginning.

Does anybody has an idea?

Thanx