IIS is set to 32-bit mode on Windows Server 2008 64 bit operating system when installing Symantec Endpoint Protection Manager. This can also occur if another website is subsequently installed that requires 32-bit compatibility (for example, Windows Server Update Services (WSUS).
Switch IIS to 64 bit mode
Open IIS > Application Pool and look for Default App Pool.
Right click on DefaultApp Pool and choose Advanced Settings...
Change the “Enable 32-bit Applications” to False.
This should disable the 32-bit functionality & enable the 64-bit functionality.
NOTE: BY DEFAULT "Enable 32-Bit Applications" is set to FALSE.