Hi,
If your requirement is like that depending on System Date you only accept Next Year of current System Year.
In time of validation you will check Text Box value is Equals to
System.DateTime.Today.Year+1
or not if not then throw some validation error
:)
If you try it on web then OnLoad put current Year value at hidden field On in Session On Cookie and Then On Submit check using Javascript by writing some javascript.
Do you need that java script