XenServer 6.1 is already up to it’s second hotfix. With the release just a month ago this is going really fast.
This hotfix has just 2 fixes it is making so here’s the long list 
:
- Attempts to move a Virtual Machine (VM) or a Virtual Disk using XenCenter 6.1, may be unsuccessful and cause XenCenter to crash, with an error message: There has been an unexpected error.
- Using non-root accounts in XenCenter 6.1 to perform operations such as starting a VM, on a host running XenServer 5.6.x or earlier, will display the No roles able to perform API call event.from error message and eventually cause XenCenter to crash.
You can download the hotfix from the Citrix website here.