"Marrying a sim in your employ would be innapropriate"

I had this with my sim. He was trying to propose to Nina Caliente but the propose was greyed out and I was getting the inappropriate to marry an employee message. Thing was she was unemployed, but they had worked together in the science career. I got her to propose and that worked. He was also in a relationship with Cassandra Goth at the the time so not sure if either or both were affecting it.