Disappearing MC

Howdy all
I’m using simple tell targets and set prop (visibility) to control some mc’s on the stage. There is a forwards button and backwards button. Each button controls 5 mc’s. The first click on the forward button and everything works okay. After using the back button then going back to forwards button one mc doesn’t appear.

my script for the first but (flash 4) looks something like this…

onmouseevent
tell target (/mc)
set prop/vis
go to and play
end tell targ
etc.

then repeated for each m/clip

would someone please let me know why this mc doesn’t show up second time around??