If there is a way then I would be interested.

I have some ASP page that just dumps the properties of the error out to a text file. You just need to set it as the Custom Error page for 500.100 errors.

Thinking about it, it might be possible to append the W3 log file, but I suspect it would be locked by the IIS process. You might be able to get to it using an ISAPI filter, but that is a bit beyond me.

edit: Here's some example code for getting error properties from an ASP page. This is saved as something like 500.asp and set as the custom error page.

Response.Status="500 Server Error"
Response.Write("<h1>whoops we have an error!</h1>")
[......]
Set objError = Server.getLastError()
strNumber = objError.AspCode
strSource = objError.Category
strPage = objError.File
strDesc = objError.Description
strCode = Server.HTMLEncode(objError.Source)
strLine = ObjError.Line
strASPDesc = ObjError.ASPDescription

I usually log the Request.ServerVariables("HTTP_REFERER"), Request.QueryString and Now() so that it can be easily tied back to the log files if required.

Gareth