Hello
Did you set the environment variable or did you unset it ?
If you see this link it suggests to unset it if the environment variable is NLS_LANG
http://www.dba-oracle.com/t_ora_12705_resolution.htm
Secondly can you list all the environment variables set for the sidadm user ?
Also provide the Oracle Instant Client version (not the Oracle version)
Check this SAP Note for more details
Note 998004 - Update the Oracle Instant Client on Windows
You need to first check the dbclient.lst file present in the kernel directory. This file will list all the files that are part of the Oracle Instant Client which will be present in the Kernel directory.
You can find the version of these files by checking the Properties - Version
Regards
RB