More than once, I've had an AOL installation on Windows fail catastophically with complaints about a missing or corrupted main.idx file. The failure occurs when you try to launch AOL, and you tend to get a series of vague error messages about startup difficulties. AOL won't start at all, and after retrying a few times, you start to see the message referring to a corrupt or missing main.idx file. These errors may coincide with address book problems; that is, you may notice some flakiness with the address book before the system gets corrupted to the point that AOL won't start at all.
The first time this happened to me, I dutifully followed the instructions and reinstalled the AOL software. After it happened again, I started looking around the system to see if I could figure out what was causing the problem or perhaps even come up with a way to repair the damage without resorting to a full reinstallation of AOL.
To my surprise, I found that AOL keeps a copy of main.idx in a backup directory! How the software can be written to keep that file backed up but then be unable to retrieve it is a mystery best left to the AOL developers, but it does result in a simple fix for main.idx issues.
Here's the fix:
If this happens to you, you might want to consider making a safety copy of main.idx somewhere completely outside the AOL folder hierarchy. Only do this when you have AOL in a sane state that starts up properly, of course - there would be no point in safeguarding a screwed-up main.idx file.
I have no idea what causes main.idx corruption problems, and at this point I don't much care - as long as this fix seems to resurrect the application, I'll stick with it.
DISCLAIMER: This works for my AOL 7.0 setup on a Windows ME box. Your mileage may vary. Any time you start screwing around with application files like this, you undertake the risk of worsening the situation and/or failing to fix the problem.
And.... now you know!