Help please

I just took charge of Middlesbrough 12 games into the season after leaving another club, it is the beginning of November and Free/Loan transfer windows are still open..

I have agreed 3 loan deal to join immediately. They've just arrived but it will not let me register them in my squad..

Anyone have an idea why or a way around this?

That's because there are player registration windows. You can't alter your registered squad outside of these windows. However, I'm pretty sure the rules state that you can register players signed on a free outside of these windows as long as you have empty spaces in your squad.

I'm guessing you don't have spaces, in which case it won't let you register them until the next registration window. I think the registration windows are identical to the transfer windows, so you'll have a couple of months to wait.