ISAPI plugin error

Hello,

I am new to working with Weblogic so I have a question...

My Production Environment is using Weblogic 8.1 With service pack 2 and Proxying
with Microsoft IIS 5.0 as a ISAPI plugin.  Earlier today we began experiencing
an error being returned from the ISAPI plugin.  The error reads something
like...

HTTP/1.1 500 Internal Server Error Connection: close Date: Mon, 28 Apr 2008
16:08:05 GMT Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET Content-Type:
text/html 

Message from the ISAPI plugin:
Internal Server failure, ISAPI plugin. Cannot continue.

Build date/time: Oct 25 2004 

Change Number: 452998

The problem seemed to clear up on it's own without having to restart either the
Weblogic or IIS server.  Can someone tell me what might be to most common cause
of this problem and where I might be able to look to find more info?  Is there a
serverl og file I can view that might give me some info?