Symptom: When running the server with multiple Web applications (either Web Connection or ASP) the browser eventually displays a blank white page with an error 270 displayed at the top.

IE 5 may simply show the standard IE error page - so if you get the 500 error page you might want to use another browser (such as Netscape) to get the actual error result page.

This problem is an unofficially acknowledged bug in IIS 4.0 (and also IIS 5) and unrelated to Web Connection. The error can also occur with ASP only applications or any other ISAPI application that utilizes COM objects and scriptmaps. The problem is caused by an error in the ISAPI subsystem that causes problems when thread context get corrupted inside of MTS hosted IIS Web sites. The problem can be addressed by making IIS not run inside of MTS packages by unsetting the Separate Memory Space option (NT) or the Process Isolation settings (Win2000).

Part of this problem got fixed in NT SP 4, but if you have a machine that had installations of SP3 or prior service packs this bug may persist even with newer SPs. Brand new installs of SP4 or later don't see this problem. Unfortunately the bug has returned in IIS 5.

There are a couple of things you can do to work around this problem:

Windows NT:
Make sure the virtual directory or Web root where the Web Connection ISAPI DLL (wc.dll) runs is not marked to 'Execute in Separate Memory Space'. I would also suggest you set the Web root to this same setting as this MTS environment is responsible for bringing out the 270 bug.

Windows 2000
Windows 2000 by default installs with an IIS Isolation mode of Pooled, which basically runs all ISAPI extensions in a single MTS session. This setting also causes the same 270 bug problem with script maps and COM applications. The best way to fix this problem is to set any virtual directory running the wc.dll to in 'Low Process Isolation' which makes the ISAPI extension run in IIS's native address space as designed by the original ISAPI spec.