Your syntax is correct, so let's run through some obvious possible problems that I wouldn't be able to see from just the expression.
1) Most obvious, make sure your dimension is indeed "year" and not "Year".
2) Make sure input box is updating variable
3) Make sure LineSalesAmount responds to selections on year dimension
4) Make sure vYear equals just numbers, and not "=2011" or something like that, with an extra, unnecessary equals sign.