Inactivate employee supplier

I am trying to inactivate employee type suppliers that have been terminated in HR.  I read that I can run the Employee Update Program to do this, but I tried it in my test system and it didn't work.  When I try to put the inactivate date in the supplier form, I get the message:

Supplier record cannot be updated.Either the Employee ID/Info is incorrect or

the employee associated with this supplier is terminated

Does anyone know how I can do this through the application?  I don't want to have to try to figure out how to use an API.