How do I extend VHD on Hyper V as RPC error received?

I am attempting to extend the IDE virtual hard disk on my virtual sharepoint server to create more space. When I go in to Hyper V Manager after shutting the VM down and chose edit virtual disk it generates and the error message:

Unable to edit the virtual disk E:\folder\server.vhd. Cannot connect to the RPC service on computer “localhost”. Make sure your RPC service is running.

I have checked the RPC service on the host is working. The host is Windows server 2008 with Hyper V installed as a role, the VHDs are stored on the E: drive of the server.

Any ideas would be great as I have a VM rapdidly running out of space!