Player/staff refuses to sign for no reason!

Here's an example - in my last save I entered contract negotiations with Angelos Charisteas, who is available on a free with no other interest apart from me. After several rounds of negotiations we agreed terms, then a couple of days later he signed for me, however I realised I'd accidentally done something stupid with one of my young players. As only a few days had gone by and I hadn't played any matches (it's pre season) I thought I would just reload and play those few days again. However now although Charisteas agrees terms successfully every time he will not sign for me! I just get a message in my inbox saying he rejected the offer, with no explanation as to why. This has happened a few other times when I've agreed terms then people have subsequently rejected me, but never when I've actually managed to sign someone previously! What the hell is going on?!