-8018: Index name must be unique

Explanation:

...

       1.      This error message can occur when a DROP INDEX statement is executed. Indexes with identical names were created for separate tables. Therefore, the name of the index to be deleted is not unique.

       2.      There is only one named single-column index for this column. An attempt was made to delete the index for this column without specifying its name.

User Action:

...

       1.      In the DROP INDEX statement, specify the name of the table to which the index to be deleted refers.

       2.      Delete the index, specifying its name.