Re authorised computer - cannot open previous epubs - please help

I was unable to check the 'Authorization Information' on my computer (option was greyed out), so I erased authorisation and then re authorised my computer in Digital Editions (to make sure correct account).

No I cannot open my previously purchased books. I was just reading it this morning before I did this. Instead I get the message 'The vendor account you entered is not associated with the item you are trying to open. Try again'.

Can anyone help? I tried chatting to support but they told me I can only get help on the forum.

Thank you