If both 32-bit and 64-bit Oracle is installed:
1. Be sure that the 32-bit driver precedes the 64-bit driver in the PATH.
NOTE: The 32-bit driver usually has client_1 in the name of the path before the bin directory. Typically, the install will put the 64-bit driver in the path first since the server OS is 64-bit. It normally will have client _2 in the path.
2. It is preferred not to have both versions installed.