Cause
A back references was found before a sub-expression.
A back references was found before a sub-expression.
Ensure a valid sub-expression is being referenced.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e12700.htm
https://community.oracle.com/message/4006317
https://community.oracle.com/message/9884278
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