My windows laptop has both the clients 32 & 64 bit I started facing all of sudden then I reordered the path variable like below
Before:
C:\app\oracle64\product\12.1.0\client_1\bin;
C:\app\oracle32\product\12.1.0\client_1\bin;
After:
C:\app\oracle32\product\12.1.0\client_1\bin;
C:\app\oracle64\product\12.1.0\client_1\bin;
started working... Hope this helps everyone.