Sync problems with Live, weird stuff...

We were throwing a live PA this weekend, and had some major sync problems. Weird thing, everything always works fine for a hundred times in a row when testing the system at studio, but once we get on stage every other nightmare suddenly happens. I was wondering, could this be because of some electricity/power issues? Every piece of equipment starts just freaking out in ways never seen before.. Same cables, same exact setup.

Friday we used (for the first time) an Apple Powerbook (OSX 10.3.4) laptop running Ableton Live 4.1 for large loops and realtime tweaking, that was taking its sync from an MPC2000. The MPC2k acts as the main sequencer, it's solid and hasn't failed me once. The laptop however seemed to drop out of sync very easily, something that never happens at home. One other problematic piece is the Waldorf Pulse rack synth, I know it's kind of sensitive about MIDI and has freaked at home also, but when playing live PA it now seems to be near 100% certainty that it goes crazy after a couple of tracks.. so it has to go from our live rack.

But the question is: why? I'm pretty sure that the MPC2000 + Ableton Live combination is a pretty used one with success, so what could cause this to us? Even the Powerbook seemed to twitch a couple of times during the live set, kind of freezing for a brief moment then trying to catch up the sequences..

Here's what we use at the moment. I'd be interested to hear from you if you have live PA experience with same kind of gear, how does it work for you?

Apple Powerbook G4
- MidiMan Midisport 4x4 - I know it's crappy, could be one reason for sync problems (takes its power from the USB)

- M-Audio MobilePre USB audio interface - another suspect

- Evolution UC33e and Oxygen 8 - controllers, no problems here, may be connected with external power supply or straight via USB

Akai MPC2000XL
- main sequencer, master sync

Waldorf Pulse
- sequenced in Ableton Live

- problem: when on stage, notes keep stucking and playing forever very easily..? Turning the thing off for a while is the only cure - for awhile..

Effects + mixer - well, no problems here..


Would be grateful for any tips, thanks!