When running a freeroll (Buy-In under Cash-In Methods is unchecked, or the Amount to Prize Pool is zero), after players are bought in they can't be seated.
They're not bought in as far as the program is concerned. Zero dollar cashin methods don't work. I need to build in some more functionality to make this work. Workaround for now would be to use $0.01 for your buyin amount. Won't be completely accurate, but close. I'll try to get freeroll functionality built into the next release.