The user filter command could not be executed.
Check that the command exists in $ORACLE_HOME/ctx/bin, and that it is executable.
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Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/drgus.htm
https://community.oracle.com/message/3916203
https://community.oracle.com/message/1636622
https://community.oracle.com/message/1634355
https://community.oracle.com/message/4454001
https://community.oracle.com/message/36843
https://community.oracle.com/message/151195
https://community.oracle.com/message/154584