My trusty, now backup, PC --- Win7, GTX 660 --- has done GPUGrid for five years with no problems. Now....

Here is the current status. No GPUGrid WUs done since April 9, but it's happy running Einstein.

I watched the download of e8s1_e3s1f9-GERARD_FXCXCL12_LIG_6730233-0-1-RND5053_1, 15 Apr 2015 | 15:29:45 UTC, but it not execute, though flagged as "Error while computing".

Help!

Disconnect, inspect, (and if there's no burn marks, smoke remnants or blackening on any pins or sleeves) reconnect all (MB+CPU+GPU) power connectors inside your PC. If your PSU is modular, you should check the other (PSU) end of all power cables as well. While doing this you should pull out your GPU from the PCIe slot, and check its golden contacts for the same signs.
If they are all ok, try the general software troubleshooting.

Thanks Retvari!

Looks like item 1. in you troubleshooting recommendations hit the spot. Panda AV had quarantined acemd.847.65.exe !!

I set it as an exclusion and await a WU download...

Bingo!! I'm running a NOELIA.

Problem solved. :) :) :)

I wonder how many other crunchers with Panda have hit this problem and given up.

Perhaps the project should have a word with Panda...