What was the precise error? A few pictures might help. I don't thing there's any reason why you can't use a Collpitts oscillator with this flow. You probably need to have the vco_vss source on your testbench, and to create a Vss pin on your "DUT", even if it is not used.
You can still have it in the testbench but not connected to anything. That's what I was suggesting. You also didn't post the error as I requested. As I said before, pictures would help.
The error message gave an important clue...you ran out of memory. Please type in an xterm
spectre -h rfmemory
like it suggests in the error message. There are a list of suggestions for you to go through. If you continue to have difficulty, I suggest contacting Cadence Customer Support.