By default, MFC uses the resource handle of the main 
application to load the resource template.
If you have an exported function in a DLL, such as one that 
launches a dialog box in the DLL, this template is actually 
stored in the DLL module. You need to switch the module 
state for the correct handle to be used. You can do this by 
adding the following code to the beginning of the function:
AFX_MANAGE_STATE(AfxGetStaticModuleState( ));
This swaps the current module state with the state returned 
from AfxGetStaticModuleState until the end of the current 
scope.

If all your resources lies in the single DLL you can even 
change the default handle to the DLL handle with the help 
of AfxSetResourceHandle function

When building a regular DLL that dynamically links to MFC,
you need to use the macroAFX_MANAGE_STATE to switch the MFC
module state correctly. This is done by adding the following
line of code to the beginning of functions exported from the
DLL:

AFX_MANAGE_STATE(AfxGetStaticModuleState( ))

The AFX_MANAGE_STATE macro should not be used in regular
DLLs that statically link to MFC or in extension DLLs.