I have an 8-core, dual ati 5770, 32gb of ram, Mac Pro 2,1 running MacOS 10.7.5. Complete Specs here... https://milkyway.cs.rpi.edu/milkyway/show_host_detail.php?hostid=749279
GPU tasks have operated properly in the past, and still work properly in seti@home. However, now I am generating computational errors for all GPU tasks in milkyway@home. This is my favorite project so I am eager to get it going again. I have switched from boinc 7.8 back to boinc 7.2. I have removed and reinstalled the project. This is a fresh install of the os. The only thing I do on this computer is boinc.
Please give your best advice here.

As I have the same problem with the 5770 & 5870 I slowly have changed over to other video cards as there doesn't seem much support for Darwin OS or AMD video cards. Look at 'Computer breakdown by operating system', doesn't even count in stats.

I have an 8-core, dual ati 5770, 32gb of ram, Mac Pro 2,1 running MacOS 10.7.5. Complete Specs here... https://milkyway.cs.rpi.edu/milkyway/show_host_detail.php?hostid=749279
GPU tasks have operated properly in the past, and still work properly in seti@home. However, now I am generating computational errors for all GPU tasks in milkyway@home. This is my favorite project so I am eager to get it going again. I have switched from boinc 7.8 back to boinc 7.2. I have removed and reinstalled the project. This is a fresh install of the os. The only thing I do on this computer is boinc.
Please give your best advice here.

Since ALL it does is Boinc you could load a Linux OS in a Virtual Box and try running MW that way, the problem is Apple and the version of something that I have forgotten the name of that Boinc needs to crunch, Apple won't let Boinc update it and it won't crunch right without it being the right version. This was discussed on Einstein too and some of those people are in the same boat you are.

On the other hand you might try the SRBase TF tasks, I ran them on a piece of crap pc that didn't even have the gpu drivers loaded one time and it worked, it owrked much better once I loaded the drivers though.