There is currently a bug in rmgpy/solver/base.pyx:

" from pydas.daspk import DASSLError as DASxError"

in one of the first code lines. This should read

" from pydas.dassl import DASSLError as DASxError"

Otherwise, if daspk is not available, the program will still try to access pydas.daspk.
This applies to the latest commit on master as of Feb 11 2021.

Best regards,
Mark