It would be much easier if you could post a small sample app that demonstrates your problem.
One possible issue could be the fact that you defined a variable start Date that seems not to be the same you are using in the expression (VstartDate), and is probably not valid syntax anyway (I think you should use a single word literal as variable name). Then, you defined the variable using a date in 2000, but your BUDAT dates start in 2010, as far as I can see.
There are lot's of other possible issues (e.g. depending on your data model, the context you want to use the expression in, syntax errors, etc).