Can you try running the command directly on command line while updating the username/password? Is your user name correct in the command? I suspect either your username/password is incorrect or some problem in invoking sqlldr from the terminal ODI is running in.
sqlldr "control='/path/sample_table.ctl'" "log='/path/sample_table.log'" userid=user/<@=snpRef.getInfo("DEST_PASS") @>@tnsentry
I stated previously that I was able to run it from term (UNIX command line) successfully.
Anyway, the solution was to create a batch in the ODI bin directory to export ORACLE_HOME path.