DLL Compatibility - VC 2003 vs VC 2005

Are there any known compatibility issues between the following?

1. Application compiled and linked with VC 2003, using CRT statically linked, AND (a) A DLL that the app uses, compiled and linked with VC 2005, using CRT statically linked, (b)A DLL, compiled and linked with VC 2005, using CRT in a DLL.

2. Do the answers to the above differ, depending on whether the app uses single-threaded or multi-threaded CRT?

If all DLLs just use PODs and does not free memory that was allocated in a foreign module there are no incompatibilities. Also don't try to export clases as a whole.

Problem arises when you want to exchange STL, CString objects and other non-POD objects.

Just to add this: You can not mix DLLs that use different shared MFC versions!