Some Web services run ISAPI DLLs on IIS 8.5 on a Win Server 2012 R2 Standard box: Classic / No Managed Code / 32-bit emulation.
The sites have been running smoothly for years on Server 2008 / IIS.75.
Recently, we migrated to the new server running 2012 / 8.5 and a site behaves very strangely:
It runs the ISAPI DLL from a different directory than the one designated – from the physical directory of another site on that server, which is completely disabled. I confirmed it conclusively in several ways. That's what happens – there is no doubt about it.
The application pool, site settings, handlers, ISAPI restrictions, and so on. are all configured correctly to point to the correct DLL – checked multiple times. applicationHost.config also displays the correct paths for the DLL to run. But it does not run – the other DLL is called instead.
The target URL is correct and the other site, where the DLL is running, is fully disabled.
I have configured several sites and I have never encountered anything like it.
What could be the cause? What did I miss?