Table maintenance generator, header name missing

I have recreated a table maintenance generator after adding two new fields, by the below process.

1. Go to the table maintenence generator from SE11, in Change Mode.

2. Click on change icon. The system will show the 'Change Generation Elements' screen where it sill ask you the resson

for change.

3. Click on the New Field/Sec. table in struction (or whichever is appropriate/applicable in your case)

4. Press Ok (Tick sign).

5. Then it will show you the ''Change Generation Elements: Detail' screen.Here;

=> You will select the maintenance screen that you wish to change( Overview/Single).

=> And the Field Type. Whether it is a key field or normal field.

Then the new field name changes to '+' sign, how can I give the appropriate name to the fields?

Please help!