I managed to track this one down, although SGPro seems to be the only program that gives this error.
In normal operations with SGPro, I save all my images to an NAS that is mapped as a local drive. This lets me get to the data from any pc in my network and having 12 TB of space beats the mostly filled 250 GB partition on my notebook. I have had no problems using SGPro as such with my QHY cameras. The last time I tried using my T3 to image, I did not have the NAS. I do not have a problem writing the Canon T3 images directly to the NAS from other software when I tried to troubleshoot this.
So, in a whim, I changed the directory to a local one and an SGPro sequence worked with the T3. I can assume that SGPro uses a temp folder on the SGPro disk to save images for centering and frame and focus. This is why I did not have any problems with these, even with longer exposure to match the sequence. But it saves to the selected drive on the NAS during the sequence that caused some problems with the Canon SDK that SGPro uses.
So for me, if I use the T3 to image, I cannot save to the NAS. Don't know if others have seen this, but the work around is simple...just got a few bumps on my my head from banging it against the desk trying to figure out why it's not working as usual.
Thanks,
Frank Z...