Hi Francois,
thank you very much for your help. We really appreciate it.
With your input we now don't need to go with eeglab anymore, so this is already a lot more convenient. Regarding the error message, we also made some progress. The fmincon function is from the Opimization Toolbox and it is the only one on the path. Also we went back to default on the Matlab path. We still get the same error message. When we run the other approach "fminsearch" the SPRiNT protocol however runs smoothly and finishes.
So do you think this is a Matlab related problem or a problem with brainstorm or our data? If it is with Matlab I could definitely open a Bug report, however I would like to hear your opinion on this first.
Thank you very much!