Error Message when saving to repository

Description of the problem:

I’m running an experiment with several participants at the same time. Sometimes I get this error message at the end of the experiment:

Any ideas / help much appreciated!

A small update:
The error message above does not seem to caus the file not beeing saved. I did get that one in the repository. However this message:
grafik caused the file not beeing saved (obviously). Could the reason be, that the participant didn’t enter a participant number? Any other possibly reasons?

Thanx