Backup you entire profile, just to be safe (
http://kb.mozillazine.org/Profile_backup ). The concept we're working from is that the current address book file is fragmented or corrupted and should be rebuilt to correct the issue. Before starting the procedure below, be sure to backup the Thunderbird Profile or at least all files in that profile that have the extension .mab.
1) Open Thunderbird's Address Book window and create a new Address Book (File->New->Address Book). Name it anything except Personal Address Book. (I would call it Temp Data to indicate it's purpose.)
2) Click on the your current Address Book (I'm assuming it's called Personal Address Book). Now click on any name in the right hand list pane. Press Ctrl-A or use menu path Edit->Select All to highlight all entries.
3) Drag-and-drop the data to the entry in the left hand pane for the new address book. This will copy over all of your address information. Check a number of the contact entries in the new address book to ensure that things have been copied correctly.
4) Now repeat highlighting the contents of the Personal Address Book, then press the delete key to erase the information in that book.
5) Close and restart Thunderbird and open the Address Book window.
6) Highlight all of the contacts in the Temp Data (or whatever you named it) address book and drag-and-drop the data to the Personal Address Book.
7) Close and restart Thunderbird and begin using the "recreated" Personal Address book for addressing messages. See if there has been any improvement.
A variation on this process would involve creating a new profile (
http://kb.mozillazine.org/Profile_Manager ) , which you would not plan to use, in order to generate a new, empty Personal Address Book file (abook.mab). Then, follow the steps above through step 3, after which you would close Thunderbird, navigate to the Profile for the real account in question, delete the file abook.mab and copy over the file with that name from the newly created profile. The result is a properly formatted abook.mab file with no contents and no file corruption. Follow from step 6 to complete the data transfer, then use Profile Manager to delete that new profile.
