Gibbygoo just sent me a PM asking if I was still having problems. I realized my reply would probably be useful to others, so here it is copied into this thread:
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Fortunately I've found a solution. Here is what I had to do to fix the problem. I spent $60 on one of DT's RWS rear skewers:
http://www.universalcycles.com/shopp...s.php?id=16375
These skewers allow you to apply a lot more torque when tightening them, due to their ratcheting system. Unfortunately, I found it to be quite a challenge to keep the wheel aligned in the dropouts while tightening the skewer.
So instead I tried taking the QR nut from the DT skewer (which has some nice, aggressive teeth) and put it on the stock Shimano skewer the Casseroll came with. By using that and tightening the Shimano skewer down reasonably well, the wheel has stayed in place perfectly.
I hope this helps. I love this bike and am glad I was able to figure out this solution.
Scott