_ATL_MIXED
_ATL_MIXED specifies that your ATL application is comprised of native and /clr compilands.
_ATL_MIXED
Remarks
When building an application that uses ATL, and where the compilands are not all native or all /clr, then you must add this macro to each compiland.
#define _ATL_MIXED
This will cause all startup code to run as native. You may need to ensure that all startup code is native. See Initialization of Mixed Assemblies for more information.