I don't kmow where the problem lies, but will put it here and in AQUA forums.

Am running 6.10.16 on vista system with a cpu witn multiple CPUS. It looks like when Aqua project runs it uses two CPUS which is fine, but after it is rotated out, only other tasks will run one at a time.
Stopping and restarting the manager and client makes no difference. Rebooting the computer resets something so that I can run multiple tasks at a time.

Any Ideas??

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Yes. I put in a bug report for v6.10.13, complaining that that version was too quick to pre-empt single threaded tasks in favour of multi-threaded (AQUA) tasks, to the extent that AQUA tasks were often starting the second they'd finished downloading.

David Anderson put in a quick fix before he left for Europe and The 5th Pan-Galactic BOINC Workshop, but the cure is worse than the disease. As I started to type this post, I was watching a quad-core running a CUDA task, one CPDN Beta, and nothing else. [It's now switched fully to AQUA, which at least keeps (most of) all four cores occupied].

David needs to have another go at this when he gets back: in the meantime, I prefer v6.10.13, even though it makes AQUA look a bit of a bully.

See also Weird Behaviour when AQUA is suspended on the AQUA boards.

Ah! Thanks, answered my question too :) I take it v6.10.16 is (seemingly) ok for computers not connected to projects with multi-threaded tasks then?!

Just for the record, I had one idle core on a multi-project quad-core. Restarted BOINC service and got 3 idle cores :( restarted service again and it used all 4 cores on aqua. Downgraded to v6.10.13 then :)