When creating a new DataType, inside the "Name" text box a String "Insert a name" is shown.
That string is a tip, and as such should be shown, but in reality it is the actual value of that text box.
That leads to
1) when editing, the user have to cancel that string before (not expected, giving the shown message)
2) if not edited, the name of the field remains the proposed one.

If that proposed string should serve a s default/auto generated value, it would be better no not use a "do that" sentence.
Attached screens.
If a "do that" string is to be used, then it should be shown as in the "Search data type" search combo