De-authorize Digital Editions

I'm Dutch and I'm really bad with computers, but I need help. And Customer Care couldn't help me.

My Digital Editions doesn't work anymore.
When I try to add a book I get the message "Error! Check Activation."

Customer Care told me I need to de-authorize and re-authorize, but in the Remove Authorization window it gives only my old e-mailadress as option, which should be changed. If I enter my password it gives the message "Can't remove authorization. Please try again later."

What do I do?