Multiple Forms Open --- Toolstrip

[C# Programming]

hi

i had a problem while using toolstrip, in C# application

i have a form named 'master', which is mdi child form.

i access it from menu click event of mdiparent form.

i have another form 'example'. it contains toolstrip.

one of the toolstrip buttons is 'master' in 'example' form.

now i m clicking that master toolstrip button again n again,it opens the 'master' form multiple times.

how can i avoid this problem( multiple forms opening)?

hope u help me in this issue.

thanx in advance,
nagendra kumar.