Today I was told about a possible problem when enabling Hyper-V Role on some HP Server models with Windows 2008 R2 installed, appears that the problem is well known in HP internal documents.
So far sounds that disabling the disabling Intel Core C3 State option in the BIOS solves the problem.
After little Google search I found this in Minasi Forum
If you’ve this problem, please let me know if that solves your problem.
I already upgrade most of my environment to R2 version of Hyper-V including SCVMM 2008 R2. I waited for the supported version of HP firmware “ver. 8.60”/software/Drivers “ver.8.30” for HP DL380G5 servers, you can find them here, after applying the new firmware and drivers everything worked fine.