FileMaker Server 9 and the "SLSocket55" Error

We're still running FileMaker Server 9 Advanced (version 9.0.3.326) on a Windows 2003-based server. At least twice in the past month, we've had incidents where all write operations through the Web publishing engine (particularly through the API for PHP) have failed. Read operations are fine during this time, and the databases behave normally when accessed by users through FileMaker Pro.

On both occasions, we've seen a "SLSocket55" error in the event log. These errors are thrown when the server reboots. The server in question is scheduled to reboot daily at 3:00am. The description of the error reads:

The description for Event ID ( 0 ) in Source ( SLSocket55 ) cannot be found. The local computer may not have the necessary registry information or message DLL files to display messages from a remote computer. You may be able to use the /AUXSOURCE= flag to retrieve this description; see Help and Support for details. The following information is part of the event: SLSocket55@localhost,ErrorCode=3021,ErrorMessage=Internal error, unable to load the server configuration file %s..

To resolve the issue, I've simply restarted the Web Publishing Engine via the FileMaker Server Admin Console.

While we are planning on upgrading to FileMaker Server 10 in the next few weeks. I doubt that this alone will permanently resolve the issue. Has anyone running FileMaker Server 10 run into this issue?