error MSB3216 when registering assembly

Closing Visual Studio and re-opening right-clicking on it -> Run as Administrator solved the problem for me.

Unfortunately there is not an easy way to do this. By default registering the components adds entries to protected keys in the registry (under HKLM in particular). This cannot be done without administrative rights.

It is technically possible to register COM components as a non-admin by using the equivalent keys under HKCU. However it is not a trivial change and I do not believe the .Net tools which register the assemblies can be configured to do this.

I think your best option is to disable registration during build. Then have a separate Admin window open where you can hand register the DLL From for debugging purposes. The re-registration is only really necessary if you change the COM related interfaces or location of the DLL so it doesn't have to be done for every F5.