Data type STRING in field &1 is not supported.

What causes this issue?

The table for which a maintenance dialog is to be generated, contains
fields with the data type STRING.
The data type STRING is not supported by the view maintenance (SE54).

System Response

No maintenance dialog can be generated. The program is cancelled.

How to fix this error?

Correct the definition of this field in this table, in the ABAP
Dictionary(SE11).

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.