Lookup Returning Wrong Value

I've attached a sample file of what I am running into issues with. I have a table of information, one column is an identifier number and the next column is the quantity associated with that identifier. The lookup is just trying to find the identifier and then return the quantity for that identify from the next column. The formula I'm using is "=IFERROR(LOOKUP(B1,Sheet1!$D$2:$E$31,Sheet1!$E$2:$E$31), "")". But it keeps either returning no number or the wrong number.

If you open the file the lookup is on sheet 2.