Access Violation when using Berkely DB in C-Language Function in VS2005

Hi,
I'm trying to use Berkely DB in C-Language Function in VS2005, following Magnus Hagander's advice, I successfully loaded BDB's library.

But when it goes to the following to statement, it shows an "int postgres.exe: access violation" error message box:
env->set_data_dir(env, data_dir);
db->open(db,NULL,relation_name,NULL,DB_BTREE,dbflags,0);

and quickly goes to line 4262 of backend/utils/misc/guc.c

This error usually ocurs when overbound, overflow or sth. like that, but I didn't figure out why?

The attachment includes my sourcefile and the scenario image. Thanks~~

Best Regards
Cristian

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