This is a problem with the 64-bit API and/or the Domino 64-bit.
I’m using NsfItemInfo to read some mime-headers.
To get the data in the original RFC2047-format, I navigate my pointer around using the RFC822ITEMDESC-structure.
In the 32-bit I would have to set struct member aligment to 1 byte.
In the 64-bit version, Domino uses the default 8/16 byte aligment, and you would normally not have to mess with pragma pack directives.
Well, except for at least one case.
The RFC822ITEMDESC structure is packed with 1-byte structure alignment.
To get around this in your 64-bit solution, you could include mimeods.h in this way:
#if defined(W64)
#pragma pack(push, 1)
#include <mimeods.h>
#pragma pack(pop)
#endif
If you happen to know a better workaround or solution - let me know 
Regards
Thomas Boesgaard