The way to decode this is to see first that it says “GetValue”. That means it’s trying to access data from the Value column of the Observations tab. “Specified cast is not valid” means that it’s finding something other than a number in that column that’s causing a problem. "GetDouble" on the next line tells you that it's looking for a number in that column. Likely, you either left the cell blank or put a non-numeric character in there.
