Red X on dataGrid display

Question

Hi

I have a data table that is bound to a data grid and is updated in 30hz - but after some time i get a red X on the display the values are still there but not displayed the message i get is :
SystemNullReferenceException : Object referebce not set to an instance of an object
But i can stiil see the values if the mouse stands on the table  but when you move it the X in Red comes back

If anyone had this bug or knows how to help me solve it i would be greatfull

Matan S