Network issue in 10.04 on hyper-v with multiple cores assigned to guest

Fresh VM installed in hyper-v server using ubuntu 10.04 LTS server cd. Using Legacy network adapter in hyper-v. When using a single core assigned to the guest it works perfectly. I do the same process with more than one core and the network stops functioning properly.
Exact behavior is that ubuntu boots and network comes alive for approximately 10 seconds then it dies. VM stays running but network drops out.
Putting the VM back to single core network functions fine.
performed all apt-get updates within the release does not affect the behavior.
do-release-upgrade to 10.10 solves the problem, but i would like to know how to fix this while staying in 10.04 LTS

Anyone?