Description:
Invalid [length] : 'None'
This means you left the cell blank.
Invalid [length] : 'eight'
This means you entered an invalid entry into the cell. For our example, we typed in "eight". Your entry will say the value you put in.
Solution:
If you have the type set to physical you must give your product a valid length.
A valid length means:
A positive number
Can use 0-9
Can use . (period)
Note: Length >= Width >= Height
For more information on length visit the documentation page.