vCenter 5.1 error: The virtual machine settings cannot be edited at this time

Hi Team,

Recently upgraded vCenter server 5.0 to 5.1 in lab, but after logon to vSphere if trying to edit VM settings get the following error.

"The virtual machine settings cannot be edited at this time. The host may be heavily loaded or the datastore on which the VM resides may be inaccessible.

If I log on directly to host using vSphere I have no problem modifying VM settings.

I have tried un-installing and re-installing vCenter server, but same error and am about to remove all but database and start again with fresh install.

I have also tried removing host's and re-adding, removing datacenter and re-creating, increasing memory and CPU to vCenter server, moving a VM to another brand new host and datastore.

If trying to edit VM settings from web agent there is no error but opens blank.