Find/Replace Problems

This is driving me mad!!

I am using find replace to change part of a formula in several similar cells and this has been working successfully but for no reason i can see it has suddenly started opening the "find values" dialog box. if i select the correct file it finds it but I must do this each time i hit replace (quite slow!). I cant use the replace all option as i don't want to replace all of them!

Please help!

on a completely separate note if anyone knows what i would need to use square brackets for in formula do let me know!

Thanks

Matt