I have both 32 bit and 64 bit Oracle client connectivity software on my machine but when connecting through 32-bit erwin Data Modeler to my Oracle Database I get error message: Unable to locate client connectivity software ora7nt.dll.

Solution:

Though you have both 32-bit and 64-bit Oracle client your path for client connection is referencing the 64-bit client .  To fix that please take the following steps

1. Go to Computer | Right click and select Properties | Advanced system Settings | Advanced tab | Environment variables

2. Go to Path under System variables

3. Double click and see if the path refers to 32 bit oracle client .The start of the path should be “C:\Oracle\product\11.2.0\client_32\" which is default location for Oracle 32 bit client.

NOTE:  if you are using 64-bit OS erwin but not the 32-bit OS erwin, then just make sure the path to the 64-bit Oracle client software is present instead.