Look at the error message: it's pretty clear:
Conversion from string 'Kitchen 41' to type 'Double' is invalid.
..................................................................
Input string was not in a correct format.
Location
is a
Double
but at least one of the cells you are trying to convert contains the text "Kitchen 41" which is not a number at all.
Use the debugger to look at your DataGrid content and determine why you are trying to convert a non-numeric value. The most frequent reason is that it's the wrong column ... but we don't have access to your data so we can't tell exactly what you are trying to do.