Fatal Error: A Matrix is not SPD


I am trying to run a SAPT0 calculation on an open shell system (using v1.3).
I have come across this fatal error message during the SAPT stage of the calculation, during or after the CPKS iterations stage (the energy and wavefunction of the two monomers were solved fine). Please could someone explain the error and how I could go about resolving it?

Fatal Error: Monomer B: A Matrix is not SPD
Error occurred in file: /scratch/psilocaluser/conda-builds/psi4-multiout_1557940846948/work/psi4/src/psi4/libsapt_solver/usapt0.cc on line: 1465
The most recent 5 function calls were:

Printing out the relevant lines from the Psithon --> Python processed input file:
core.set_global_option(“REFERENCE”, “uhf”)
core.set_global_option(“BASIS”, “aug-cc-pvdz”)
core.set_global_option(“GUESS”, “sad”)
core.set_global_option(“SCF_TYPE”, “df”)
–> energy(‘sapt0’)

Could you post the input file for this one? I’ll get the issue transferred to the SAPT developers.