Players I cannot de-activate or sell
 

Two of my teams have players that I cannot deactivate or sell. they are not the same players, all the time. I have tendency to empty out my reserve team and sell them all off, before I start looking for upgrades in the AH, but when I select all the reserve players, right click on one and choose "deactivate xx players" I get the confirmation message, but it will say "there was an issue deactivating John Doe, John Doe2" and leave those two players on the reserve team. I have no empty spots in my active roster.

You must have 15 position players on your active and reserves roster combined at all times. You can't sell players to go below 15.

OK, that makes sense.