Unable to register player untill next window

I got a problem with signing new players. When I try to make an offer for most of the player there is a message at the bottom saying that I will not be able to register this player for the league until the next window. I play Southampton and bough 3 players without any issues nut now I have this problem. Also the message is not shown on some players like Saka from Arsenal but its still there for other Arsenal or English players. Is this supposed to be like that ? What rule is there ?

i believe it's just a glitch. Same thing happened to me with Pacheco. It ended letting me registrate him my doing in manually instead

Currently having the same problem going to try jackiechan126 format hopefully it works

I've got the same issue, but worse I guess.. they don't even join my club until the next window and anyone else i've tried to buy/loan have the same issue.