If you are trying to P2V a server and VMWare converter fails with this error messge "Multiple connections to a server or shared resource by the same user, using more than one user name, are not allowed. Disconnect all previous connections to the server or shared resource and try again.", you came to right place.
Answer is very simple. You already have a mapped drives to the source machine (or at least mapped IPC$ share). So simply unmap the shares using Net Use /DELETE command. OR simply run Net Use * /delete to remove all network mappings on the computer where you run your VMVC or Converver console runs. After you deleted the network mapping, try the P2V again. It should work.
If you still have issues, remote desktop to the source machine with same account which you are using to P2V. Then try the P2V process again.