KUP-05011: Size of file

I am getting the following error while accessing the external table in oracle 12c.

SELECT COUNT(*) FROM <schema>.<tablename> EXTERNAL MODIFY(LOCATION(‘’' || IMP_FILE_NAME || ‘’')) WHERE TEXT LIKE ' || ‘’'%completed with%error(s)%‘’

ORA-29913: error in executing ODCIEXTTABLEFETCH callout

ORA-29400: data cartridge error

KUP-05011: Size of file <filename>_imp.log in directory /Oracle_Exports_NA/MONTH_06/file has changed from 533869 to 567622.

ORA-06512: at line 20

29913. 00000 - “error in executing %s callout”

*Cause:   The execution of the specified callout caused an error.

*Action:  Examine the error messages take appropriate action.

Any clue can be really helpful.

Thanks