There is a problem with DOA in C++ Builder 11.2 with 64 bit applications.
OracleSession1->LogOn() causes an EAcceVioloation:

Access violation at address 00007FFC3C6631D3 in module 'OraClient.Dll'. Write of address 0000000000000018

We are aware that there are some compiler options that can cause this issue in 11.2. We will have an update next week.

Thanks a lot!