If you have a 64-bit Oracle install, a 64-bit Server install and a 32-bit Desktop install
on the same host, you may need to add both 32-bit and 64-bit Instant Client software
to get the PATH to have the right clients in the right order.
Sometimes it helps to split up the software stack, and place Desktop on a different host,
without the database or Server components to muddle the 32-bit/64-bit evaluation order.