Check the followings.
 

• There is no text above the cursor when you selected [Numbering].
   
• Invalid character is selected for [Numbering].
  Valid values as the last number to be printed: Up to 9, higher than the number to start with.
   
• Invalid number is selected for [Tab Length] or [Label Length].
  Valid values are as follows.
  Tab Length: 0 mm - 100 mm / 0.0″ - 4.0″
  Label Length: 30 mm - 300 mm / 1.2″ - 12.0″
   
• An invalid value was entered as the label length while using templates.
  Valid values: 30 - 999 mm / 1.2″ - 39.0″