Virtual PC setup for Training PCS

What im looking for is to have around 15 pc’s run one virtual image that i have created. I dont want to have to copy that image locally on each. When i try opening two sessions i get the following message …..

“the file … cannot be accessed.
It may be in use by a running virtual machine, the virtual disk wizard, or you may not have the proper access privileges. Please select another file.”

Another have any ideas please. Thanks in advance