Why doesn't this VLOOKUP work?

Ok so in the attached sheet, column T and U have VLOOKUPS in them but neither work.

They look at the corresponding column B value. The value is in there and looks at another cell. e.g B4 get's it's value from B3.

If i type in to B4 what's already in there, e.g 1100, the look up works.

Why is this? What is wrong with using a value generated by a formula?