Unable to file 1065 Partnership Return due to Business Code

I'm getting an error on my federal 1065 partnership return saying I haven't entered a valid 6 digit business code.  In all past years I've used 531100 for my rental property but that's giving me an error.  I read an article that this number doesn't effect your return, and is just used for data collection,  that you can enter 999999 instead.  That didn't work either though. Please help!