This issue is fixed. tnsnames.ora file need to exist in the both OBIEE Oracle homes ( C:\Middleware\Oracle_BI1 and C:\Middleware\oracle_common )
After the 18.104.22.168 installation on my Windows Machine, C:\Middleware\Oracle_BI1\network\admin directory structure was created.
However for the 2nd Oracle Home (C:\Middleware\oracle_common), the directory structure existed only till C:\Middleware\oracle_common\network. I copied the TNS file to C:\Middleware\oracle_common\network. Now its working
pls mark as correct if helpful