An experiment that was running successfully in PsychoPy 2020.1.2, was then loaded in 2020.2.4, and compiled and run there. The screen went blank for a moment, and then the experiment exited abruptly. The Runner did not capture any error output. The only way to see that is to rerun the experiment manually on the command line: >python experimentname_lastrun.py
This produced a traceback ending with:
pal['lineRGB'] = pal['lineColor'] = [max(c - 0.05, 0.05) for c in self.win.color] TypeError: unsupported operand type(s) for -: 'str' and 'float'
Not very useful, but this was generated by a Form component in the experiment, and after some debugging, turned out to be due to an experiment setting.
To fix, go to Experiment Settings > Screen > Color, and change “black” to “$[0,0,0]”. The documentation indicates that named colors are supported, so this is either a new bug, or the documentation is outdated, but maybe this helps someone.