Index was outside the bounds of the array

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Hey all,
I am trying to put a text of textbox1 into richtextbox but apearently i am getting a error saying " Index was outside the bounds of the array."
The code i am using is very simple, here it is : "richTextBox1->Lines[0]=textBox1->Text;"

I wish to solve this error and know why i got it cause everything seems fine to me,
Thanks in advanced.