Table &: Conversion already started

What causes this issue?

There was an attempt to delete the table from the display.

System Response

This action is rejected by the system because the conversion was
already begun for the selected table.
Only those tables for which the conversion was not yet started can be
deleted from the display with the function used. These are marked with
@4L@ in the Table column.

How to fix this error?

The table conversion is continued.

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.