Check box in a form creates an overlap of check mark and cross...?

Hello,

I have a form that on my computer looks fine and on my friend's computer looks wrong. I created check boxes with an "x" mark, however, on my friends computer it creates a check mark AND an "x" overlapped. I'm not sure what's happening, I can't get the problem to show up on my work PC or my MacBook Pro. All help is appreciated!

Thanks!