Specified cast is not valid C#

That's an assignment, not a comparison - so the result that you are converting with ToBoolean is probably not what you expected. Probably, you meant "==" rather than "=".

But the problem is almost certainly the cast of the Value property to a bool - use the debugger to find out exactly what the cell contains, and then start look for what it should be. Chances are you are looking at the wrong column, or a empty row at the bottom of the DGV.

And your shouldn't really be using the DGV itself, but the DataSource from which it was filled; and not using "magic numbers" like "22" anyway.