Plesk License auto-renewal failures solved!

We've been battling a strange problem with Plesk licensing for several months. Plesk apparently requires your server to re-register itself with them every couple of months to make sure that its license key is still valid. If the key isn't valid, Plesk enters a grace period after which it will stop working. We've been seeing the following error whenever we try to renew the key:

Key Update Status:
Unable to update Plesk Key. An error occurred while processing your key.

You can try to update it later. The key cannot be upgraded due to the network failure during connection with the Key Authority server. Please check that your Internet connection is configured, you can resolve and access ka.swsoft.com and your firewall enables outgoing connections to TCP port 5224.

Of course, we have no problems connecting to port 5224 on ka.swsoft.com:

telnet ka.swsoft.com 5224
Trying 64.131.90.38...
Connected to ka.swsoft.com.
Escape character is '^]'.
....

The next step is obviously to call SWSoft's support, right? Well when we did that, we found out that since this server is leased from the Planet, they technically own the Plesk license and we'll have to go through their support. This is always a bad sign, when you have separate vendors support people talking to each other, they usually seem to be interested in seeing how they can lay the blame for the problem on the other vendor (and close out their own ticket). True to form, the first two times that our Plesk license was expiring, the Planet installed a temporary key and said they would follow up with SWSoft for a permanent solution. Of course, once the support ticket was closed we never heard back from them.

But the third time was the charm. Not only did I get a competent support person, but enough people had complained about the problem that SWSoft had released a document on how to fix the problem. It comes down to some corrupt MySQL rows in their license key storage table. Once those are removed, everything works just fine. Of course they never explain why those corrupt rows are there. It appears to be the same two corrupt rows for their example and our server, which makes me think that it is a widespread problem (perhaps caused by an upgrade), but I suppose that I have more pressing issues to deal with now.