Hi Irene,
My memory is that when people had trouble with this, the put a blank space between the outgroups.
The requirement is for a comma separated list, which you can enter into the cipres form:
outgroup1,outgroup2,outgroup3 for example.
If you are doing it this way and still having issues, please send me the _jobinfo.txt file for a failed job anbd I can explore.
Best,
Mark