Thanks a lot for the reply!
1) I dont want the line charts to be conditionally enabled. They should always be active and they reside in a different sheet from the pivot table. What I want is, when someone clicks on the year field of the pivot table, they should be redirected to another sheet where the line chart resides (and the line chart should become active).
2) Year is not a dimension of the chart. Its an expression thats part of the pivot table(for a few reasons, I cant make year to be a dimension, its got to remain an expression). So, I cant directly use '=GetPossibleCount(Year)=1'
Really appreciate your help.