Mac Pro (Desktop not Laptop) GUI Locks up, but cursor still moves, machine is not dead or hung

This is an ongoing problem, and IIRC it happened with my other video card under a different OS but the same Mac Pro.

Here's the messages in the console logs:

4/18/16 1:25:41.099 PM WindowServer[186]: Surface testing disallowed updates for 10 sequential attempts...

(Some people report changing the screensaver gets rid of these.)

And

4/18/16 1:25:49.000 PM kernel[0]: ** GPU ASIC Log Start **

At which point it starts dumping a bunch of this into the log file:

4/18/16 1:25:49.000 PM kernel[0]: : 0x0000679a : 0x000000e3 : 0x00000001 : 0x00000018 : 0x000090b0 : 0x00000001 : 0x00000001 : 0x0000679a 

I'm working on a couple of theories:

1. Corrupt JPEGs in my Photos that the screensaver was using. I know there are some in the library. I changed to a regular screensaver that doesn't use them.

2. Power Management problem with the video card/display/whatever so I set the displays to never sleep in the control panel.

3. I used smcFanControl to up the fan speed slightly so everything will run a bit cooler.

In the past, I had a similar problem with black screens and not sleeping the display fixed that. 

So, will update later. 

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