Sorry!!!!! I totally missed your message and was coming back to the forum to write you because I thought I hadn't heard from you...

You mean load an SPM.mat (output from a concatenated gPPI analysis for which the contrasts did not estimate) for a random subject through the SPM GUI, define a contrast, and see if the contrast estimates? Yes, I tried that and I don't get any errors through the SPM GUI.

Thank you for your help!
Gina