<zero_debts>1</zero_debts> results in a Config: zero long-term debts on startup message, suggesting this requires a system restart.

To confirm I upped the cache to 9days, tried this without restarting Boinc (ie just re-reading the cc_config file) and it made no difference.
Then I closed Boinc, waited 1min, opened Boinc and I still got,

18/03/2011 09:18:12 World Community Grid Sending scheduler request: To fetch work.
18/03/2011 09:18:12 World Community Grid Requesting new tasks for GPU
18/03/2011 09:18:15 World Community Grid Scheduler request completed: got 0 new tasks

So a system restart would be required.

If you don't want to restart the system, or reset the project, there is another way:

Suspended all other projects (I had won't get new tasks already in place). Boinc will immediately ask WCG for CPU work, if your cache is high enough.

Certainly easier than restarting the system or resetting the project just to get a few tasks

This is a usefule technique for anyone who keeps their cache low for GPU work, or wants to just run WCG tasks for a while (when Betas are about).
Just remember to decrease the cache and then enable projects again, in that order

Obviously you had enough CPU-work for WCG (or for other projects), but not enough GPU-work.
Although WCG doesn't have GPU-work available, the (stupid) client requests GPU-work from WCG, because of the WCG's long term GPU-debt.
(another way to report RtR CPU-tasks ;))

If you want to do more WCG work, increase the resource share.
If you want to do more WCG work temporarily, you could use boinccmd from a command line and increase the debts:
Example: "Path\boinccmd" --set_debts www.worldcommunitygrid.org 10000 86400
The numbers are seconds. In Boinc Manager you can see the actual debts when clicking properties of a project.

[ot]
@Mark Reiss: Because of database problems with BOINCstats about a week ago all signature-id's were renumbered.
That's why your BOINCstats-signature shows an invalid id. Others got the signature of another cruncher.
Your new id and signature is 4005.
[/ot]

Thanks for the tip, Crystal Pellet! I hadn't stumbled on that particular capability of boinccmd before, and it will come in handy.

Don't be anxious, Sek

The calculation of the debts was always a subject for David A. for reprogramming BOINC.
Your right about the fact it's not that simple. In version 6.10.58:
The short term debt (STD) can be positive or negative, but the sum of all projects is zero.
When I set the STD for WCG to 3000, the debts of all other projects will be lowered so that their sum together (+ or -) will be -3000.

The behaviour for the long term debt (LTD) is a bit different. Only active projects with tasks in your list are recalculated.
Also different is that the maximum of the LTD is zero, so in my example in the former post +86400 for WCG will be changed to 0
and the LTD of the other active projects will be lowered in a proportion depending of their resource shares.