I figured out that all of my tasks that had validate errors, were those that had already previously had a validate error on some other computer. So, I went through one-by-one per host, located all the offenders and aborted them. No more validate errors and a lot more RAC is the result.

Oddly, my old processor that's over-clocked to 2.4 is getting better credit awarded than the processor running at the stock 3.06. Could it be that over-clocked hosts get preferential treatment on this project? Are credits awarded based on stock cpu freq despite what the cpu is running at?