The error message means Adobe (at least the ADE part of it) don't know how to write proper software, or can't be bothered to.
It is probably due to a bug in ADE2.0.
See for example Every single problem I have experienced with library books and BAD LOAN messages is the fault of ADE 2.0. from the thread http://forums.adobe.com/message/4831892
ADE2.0 is absolutely riddled with bugs which Adobe has shown no sign of wishing to fix. I hadn't seen this particular one before.
Install and use v1.7.2.
You may not be able to return the books you have already borrowed with ADE2.0, but at least it should go smoothly with newly borrowed ones when those expire.
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
I agree with the rest of the post I quoted above:
It is remarkable how deeply flawed the update is and equally how ADE tech support attempts to resolve their own issues by attempting to charge $68 to find the problem in their own software. Frankly I was really disgusted to see that the problem was their issue and how little they have done to correct it after months of questions and complaints from their own users.
Make sure that you have authorized your PC ( under help in ADE) . I had the same error E_BAD LOAN_ID and as soon as I entered the authorization ID (basically the same user id and a password like you use for the forum here ) the problem went away.