Can't Return a borrowed book

[_Vickie_Melograno_]

I use Adobe Digital Edition to read E-books downloaded from my library. I've checked out many books over the past few weeks, and when I've finished them, I've returned them with no problem (by clicking on "Return Borrowed Items"). However, I recently checked out two books, and I can't return either of them. When I click on "Return Borrowed Items," I get this message:

Adobe DRM Error
System: 5
State: 4
Class: 400
Code: 61
Message: Error on response from server.
Scroll below or view error.log for more details.
Could not authenticate with voucher engine at server
Server Code: 400
Requested URL:
http://207.54.136.76/fulfill/ebx.etd

400 Bad Request
(35) Problem at step 2 of return request:
Unable to early return eBook

--- end ---

Does anyone know what this means and how to fix it?

[_Greg_Petersons_]

We are sorry for the problem that they have encountered. You are
experiencing this error because your have returned an excessive amount
of titles in a short amount of time. Please try again in a couple of
days to see if that resolves the problem. Thank you.

[Guest]

Did you ever find a solution to this problem? I am having a similar problem. Thank you!