how to change the driver of a ole_dbconnection from oracle_32bit to oracle_64bit
Even in this day and age, Windows is still reliant on the good, old-fashioned DOS PATH environment variable for finding dynamically linked libraries (DLLs).  

It is possible that the 64-bit installation has altered the PATH variable (usually to insert its own location at the start of the "list").  This means that the 32-bit application, while searching through the DOS PATH, will find correctly-named 64-bit libraries before the 32-bit ones that it requires.