Hi

My data is in range B7:F8. Row 7 and 8 is merged (B7/B8, C7/C8 ... E7/
E8) is merged. Therefore in all I have five cells.

I want an input "X" or "x" in one of those five cells. (Only one
input, more than one is not allowed)

If anyone gives two inputs
OR
if anyone types anything besides "X" or "x"
OR
if anyone types anything of length more than one character

It should give a validation error box with a message.

Can someone give a formula to enter in the validation box?