I AM NOT IMBECILE YOU ARE AND I KNOW WHAT THAT WORD MEANS!
Can't work out why I can't castle

You can't castle when your king is in check, when your king ends up in check, or when your rook ends up in check. The last one is the case here.
EDIT: You also can't castle when your rook has moved, or when your king has moved. In case you didn't know.
Perplexing. Members posting help who have not a clue about the rules - providing false information.
Always best to perform due diligence and search the sites resources 1st. Castling rules are clearly written.
The King may not pass through a square that is attacked by the opposing side - as it would be captured - as in being in check.
That’s a doozy- weird idea about the Rook being in check.

I should have said when the rook ends up being attacked. Of course the rook can never be 'in check'. Lol brain fart.
And they still get it wrong !!
Simply play Rd1 winning the Queen for the Rook as they Black King is pinned.

Best practice here is to post a link to a bona fide source. For example when questions arise regarding rules link your answer to FIDE Laws of Chess or chess.com How to play chess/rules
see post #6
Oh and I looked at your profile and it's pretty good and you'd probably beat me but there's a lot of daily games is that because your too scared to get beaten in 1 game???