Ok the answer to Round 20 was....
Square number 4!!! I KNEW IT WAS!!!

Also well done this week to the following people who also guessed correctly that the ball was in square 4 :
vorlon24,
slater_scott,
Steven, "On a roll"
Rebecca G 
and of course
moi
Spot the Ball league table has been updated to include Round 20 and can be seen in the usual thread...
Jimbo T

blower