Hi Marco,
The bitness of the Oracle precompiler should not matter because it is only creating .c files from the .sqc files and not used to build binaries. However the Oracle client runtime library bitness would be relevant to the final application build and execution.
If you are building a Gen Window packaged application i.e GUI application containing SQL calls then it will always be a 32-bit application and you need the 32-bit Oracle client software.
If you are building a Gen Cooperative packaged application and the Server Manager is making the SQL calls then it can be 32-bit or 64-bit depending on compiler version and BT profile settings (OPTIONS>OPT.BITS), so you need to install corresponding Oracle client software.
Assuming this is a Window packaged application for now for the error you are seeing it seems to be trying to look for the precompiler executable proc.exe in the Gen install directory which is not correct because the Oracle client software should have its own install directory.
The BT Profile options for DBMS>Oracle should be set to where the Oracle client software is installed. That is also per AndyHebert 's advice in your earlier thread: PROC.EXE not found
See this example for my test environment for Oracle 11g 32-bit client which you mentioned in that earlier thread.
If you still have problems please upload the complete .out file and screenshot of your BT profile settngs
I hope that information helps
Thanks
Lynn
NOTE: I saw your other thread saying you are using the free version of Gen 8.6. Oracle 12c is actually the default for Gen 8.6 and to be able to use Oracle 11g the Gen runtimes will need to be rebuilt with script mkdbs.bat otherwise after the application is successfully and executed I would expect the attempted connection to Oracle to fail.