"Length cannot be less than zero. Parameter name:Length" error in xaml navigation page

Question

Hello I am Rama, student from Malaysia doing my final year project in IT. I have this error "Length cannot be less than zero. Parameter name: Length" in my xaml navigation page. 

What I am trying to do is that I am trying to call a page into a main page and that page has a hyperlink which when it is clicked, a popup page should appear in that main page. This error occurs in the first line of the xaml code on the page that is being called to the main page. 

Could anyone help me out with this problem please.... Thank you in advance.

Yours sincerely, Rama.