i Have same problem i think i figure it out.
After latest patch if you transfer some rent football players and switch it between yours and his or hers you will game this issue.You can check like me you can enter old game with this link.I cant fire these rent players because you need give so much contract money. This is a database issue and developers need fix it.Try to enter the game at old system from here : Play Top Eleven - Free Online Football Manager Game