I'm having this and other problems since upgrading to U3. I have the hosts not responding, VCB problems and Vmotion problems. Everything was solid with U2 and all the problems started with U3. I have this on HP DL580 G5 servers and DL460 blades. It seems like the hosts go to sleep. The first attempt at VMotion or VCB will fail, but from that point on everything works OK until I leave them alone for a while. I've been working on it in my lab and I have increased the the host memory to 512 meg, which did not fix it. I switched the COS and VMotion NICS to Intel from Broadcom, still no fix. The last thing I did was upgrade the HP agents to 8.1.1, this might have fixed it, but I'm not sure yet. I noticed in HP's release notes that 8.1.1 support U3. So put me down as HP hardware, Intel CPUs, Emulex HBAs.