The attached file was written by SMath Studio Desktop after some error happens, which I cannot reproduce. Nevertheless I was able to save my work. But loading the saved file lead to an error:
In german: "Der Index war außerhalb des Arraybereichs." (roughly translates to 'array index out of bounds error')
I was able to work around this error by manually editing the original file I was working on. In the <region> elements I replaced 'color="#73642" bgColor="#fdf6e3"' with 'color="#000000" bgColor="#ffffff"'
The attached file is a minimal example to reproduce the error message I describe.