The GetExtensionVersion function is the first entry point IIS calls. IIS calls this function in the system context and it is called only once. This enables ISAPI extensions to register their version information with IIS.
BOOL WINAPI GetExtensionVersion(
HSE_VERSION_INFO* pVer
);
If the function succeeds, the return value is TRUE. If the function fails, the return value is FALSE. The Win32® GetLastError function can be used to determine why the call failed.