Hm, interesting dilemma. How old is he? Is the problem only with playing in his room--- or would it be different if you sent him to play in the basement or playroom? My kids have some "quiet" time every day in which they hang in their rooms. I do this to promote them being able to play independently and entertain themselves and so I can do something like, oh I don't know--- take a shower or something. It has actually been great because my kids kind of value this time and have found great ways to spend it. Your son does play elsewhere, so he knows how to play (some kids actually developmentally do not)--- but chooses not too. Are you just concerned that he isn't using his toys or that something is really wrong? In asking how old he is, that would tell a lot. Could you ask him why he doesn't want to play for a while by himself? I also found just turning the tv off and letting them start playing works really well. It might not be in his room but if you brought something from his room to your tv room, he may sit there and play with it. Also maybe a timer so he knows how long he will have to do it if it isn't his favorite activity. Not sure what is going on here but good luck solving it.
Why has he got to go up to his room could he not play where you are maybe he likes company, how old is he, I think he is asking to stay where you guys are that seems fairly normal to me its like a punishment being sent somewhere you dont want to be .Do you see him all day that you dont want him around in the evening ?"
Is he the only child? How old is your son? Becuase I know my son is an only child and that could make the difference. He will eventually move past this my son did.