Enhance Standard table HRP5121

I am trying to add one field to HRP5121 which of type "String", while activating it is givng me error

as the enhancement category for HRP5121 is "can be enhanced ( character or numeric ),

even if i add field either in CI_p5121 or append structure which again contains my custom field i am not able to activate the table though Implicit enhancement of table HRP5121 is now changed to as of CI_P5121 or append structure.

the table HRP5121 is inconsistent.

Please suggest me how can i field in this table which of type string, even if i add it and somehow activate it, still my applications are dumping as it is inconsistent