Have you allowed balance to build up, I never withdraw, so it is paid out quarterly.
Cannot find it at the moment but had a message this morning saying my quarterly payment would be made early October, so perhaps yours is already in the system for a pay out, although it is surprising that you cannot withdraw now.
I may be wrong, but it may be the explanation, although I understand it should not prevent you making a withdrawal now.
I have just looked at my balance and the facility to withdraw now is still available, have you clicked on the arrow to go to withdrawal page.