Hi,
(note: Commands etc translated from Swedish and might not correspond to 100% to your English text)

Solution 1.
the easiest way is to mark all cells (25x400), then select menu Format/cells. Select the second tab from the left ("Adjustment" or somehting like that). Under "Text control", uncheck the (probably grey) checkbox called "Merge cells".

Now there shouldn't be any more megred cells.

Solution 2.
If you want to find them and keep them, there is a way of finding them by conditional formating (using the function Column() or Row() to paint either every second line or every second row in different colour).
Tell me if solution 1 doesn't work and you need help with details for solution 2.

Kind regards
Bjorn