Event ID 19

After installing IIS on an NT 4 sever I receive this error every couple minutes. "Event ID: 19; Source: W3SVC; The HTTP server was unable to load the ISAPI Application 'C:\InetPub\scripts\..%5c..(and %2f)\Admin.dll'. The data is in the error. Data:0000: 7e 00 00 00". Our server is accessible via its private IP but not via the public IP mapped through the router (port 80). EventId.net says that it is becuase of a missing file or the nimda virus. I've been trying to install Trend Micro's ServerProtect as a part of our antivirus solution but when installing it I get an error saying that it couldn't log in. Without IIS running properly I can't install the antivirus software. I'm trying to contact Trend to see if they can help. Any suggestions?