Problem with deserialization

Question

Hi.
I create a XML configuration file for my program settings via serialization.
Program can create configuration file for the first time and read it till it is not changed.
But when I change its content via program (Program settings), configuration file creates error and says:

The XML page cannot be displayed

Cannot view XML input using XSL style sheet. Please correct the error and then click the Refresh button, or try again later.

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Invalid at the top level of the document. Error processing resource 'file:///D:/C# Examples/Calender/Calender/bin/Debug/Con...

</SettingsData>ta>
---------------^

What's the problem?
Tnx