I contacted my library' support team and they came up with a solution. However, I'm not sure it will work for those who are unable to redownload titles (from my website, I'm able to download ebooks a second time....)
This is what they said:
1. Open Adobe Digital Editions and delete the title you are having
trouble with. Then close Adobe Digital Editions.
2. Open the 'Control Panel'.
3. Open 'Folder Options' and select the 'View' tab.
4. Select 'Show hidden files and folders'.
5. Un-check 'Hide protected operating system files'.
6. In the warning message you receive, click 'Yes'.
7. Click 'OK'.
8. Close the Control Panel.
9. Navigate to the following location:
C:\Documents and Settings\(user name)\Application Data\ Adobe\Digital
Editions\
10. Delete the Voucher folder.
11. Navigate to My Documents / My Digital Editions. Delete the PDF
file for this title.
12. Also in the 'My Documents / My Digital Editions', delete the
manifest.xml file.
13. Navigate to My Documents / My Digital Editions / ebx_backup.
Delete the PDF file for this title.
**** The following steps involve modifying the registry. Please be VERY
careful and do not delete or rename anything else in the registry
besides the items mentioned below.
14. Click 'Start > Run'.
15. Type 'Regedit' and click 'OK'.
16. Navigate to 'HKEY_CURRENT_USER\Software\Adobe\Adept\Activation'.
17. Here you will see several folders, numbered 0000, 0001, 0002, etc.
Click once on '0000'. In the right pane, you should see one entry with
something in the 'Data' column. One of these folders (0000, 0001, 0002,
etc.) will have 'loanToken' for the data. Expand this folder.
18. Inside the 'loanToken' folder, you will have more folders numbered
0000, 0001, etc. Select them one at a time. You should see several that
contain a name of (Default) with Data of loan. Delete each numbered
folder (0000, 0001, etc.) that contains the (Default) loan inside it.
19. Close the registry and open Adobe Digital Editions. It should open
without error.
20. Return to the library website and try the download of your title again.
Hope this helps!