The process cannot access the xml file

Dear All,
         I have one silverlight app,on click of one button,i,m reading values from xml file and displaying in textbox.On click of another button i,m writing values to the same xml file but it was throwing an exception that:

The process cannot access the file 'D:\data.xml' because it is being used by another process.How can i resolve this problem?

Thanks in advance.