Prism 3 crashes when I try to import data using the unstack option.

Prism 3 will crash when the column numbers you enter for either the values or the grouping variable are for columns that don't exist in the data block that Prism "sees". Beware of selecting a discontinous range in Excel, and then pasting. Use the View tab to see what is actually pasted into Prism and for the column numbers you should use.