sharepoint 2010 list view Group by Year if i press Plus marks not displaying the items

sharepoint 2010 list view Group by Year if i press Plus marks  not displaying the items

I have a list, and a calculated column, i created view group by calculated column,

it shows the total number of items per each group

but when i press plus mark, it does not pull any items from that list, for testing i create one more column with year, manually added data. that time it works fine..

any help?

server: sharepoint 2010..

Guruprasad Marathe