While registering a CRM 2011 plugin I kept getting the following error in only one of our test environments.
Assembly must be registered in isolation
After a lot of searching I found out that the reason I was getting this error in only one environment was that I was not designated as a “Deployment Administrator”. Once I had that fixed, the error went away!
Unhandled Exception: System.ServiceModel.FaultException`1[[Microsoft.Xrm.Sdk.OrganizationServiceFault, Microsoft.Xrm.Sdk, Version=184.108.40.206, Culture=neutral, PublicKeyToken=31bf3856ad364e35]]: Action failed for assembly xxxxxxxxx, Version=220.127.116.11, Culture=neutral, PublicKeyToken=yyyyyyy': Assembly must be registered in isolation.