Yes - you can't bring COUNTD in data blending...In the past, I've just changed my primary table to the one with the calculation which has the "countd" in it - but obviously that may not be a solution depending on how your data sits...
I also facing the same and trying to figure out the workaround. Below links will give you more information.
It seems you CAN use countd on the primary data source. It's weird the problem was with the parameter. I was using a boolean parameter(T or F) and when i changed that to an integer type everything worked!