[LAU] jack freewheeling / has excessive timing errors

Hi all, may I ask what could be the cause of jack freewheeling unexpectedly and having timing errors (and xruns of course). the console window outputs these error messages: JackPosixSemaphore::TimedWait err = Connection timed out JackFreewheelDriver::ProcessSync: SuspendRefNum error JackAudioDriver::ProcessGraphSync: ProcessWriteSlaves error, engine may now behave abnormally!! JackPosixSemaphore::TimedWait err = Connection timed out JackAudioDriver::ProcessGraphSync: SuspendRefNum error, engine may now behave abnormally!! If I happen to run zita-a2j and zitaj2a instances at the time this happens, they will report: Detected excessive timing errors, waiting 15 seconds. This may happen with current Jack1 after freewheeling. Detected excessive timing errors, waiting 15 seconds. This may happen with current Jack1 after freewheeling. Detected excessive timing errors, waiting 15 seconds. This may happen with current Jack1 after freewheeling. Detected excessive timing errors, waiting 15 seconds. This may happen with current Jack1 after freewheeling. Starting synchronisation. Starting synchronisation. The setup I have contains the following cards: 0 [DMX6Fire ]: ICE1712 - TerraTec DMX6Fire TerraTec DMX6Fire at 0xec00, irq 16 1 [Intel ]: HDA-Intel - HDA Intel HDA Intel at 0xf9ff8000 irq 45 2 [DSP24 ]: ICE1712 - Hoontech SoundTrack Audio DSP24 Hoontech SoundTrack Audio DSP24 at 0xe400, irq 17 3 [DSP24_1 ]: ICE1712 - Hoontech SoundTrack Audio DSP24 Hoontech SoundTrack Audio DSP24 at 0xd880, irq 18 I run jack on a combination of cards #2 and #3. Analytically: It contains 2x hoontech dsp c-ports 2000 (each with 8x ins and 8x outs - these cards are identical with each other and very similar to the Midiman L1010 - same ICE1712 chip), joined as a unified sound card with 16x ins and 16x outs through ~/.asoundrc as described here http://bandshed.net/forum/index.php?topic=1208.0. I have unfortunately deviated from the guide, in that I have not used the SPDIF output of the 1st card to syncronize the clock of the 2nd one. This was not intentional but some unexpected error shows up in the envy24control when I try to set the SPDIF settings as shown in the link. So I can only assume my changes have not been registered (they definitely do not survive a restart of the envy24control mixer). The bottom line is the 2 sound cards may very well be running out of sync. Is that a reason that could cause the freewheeling? I do not get xruns messages in qjackctl often, but when a message appears the counted xruns are in the order of ~1600 or so. I am junning jackd2 with there parameters: jackd -S -R -dalsa -C capture16 -P playback16 -r48000 -p256 -n2 Should be reasonble to avoid these many xruns. No? Additionally, there are alot of plugins loaded. 2x mpd's , many calf racks (~21 calf plugins in total), pulseaudio jack module and some times zita-a2j and zita-j2a to connect in the setup the additional soundcards (DMX6Fire and HDA_Intel). The problem is that because of these timing errors some (but never all!) calf racks crash and I would like to avoid that. So what could be triggers for these jack error messages ? thank you in advance for your help.