Module: ActionView::Helpers::DateHelper

hi i am using date_select helper for displaying month day and year.I am
trying to show month and year by the options of the helper as
<%=date_select( "post", "written_on", :discard_day => true)%>

But i am getting error as
undefined method `styled_input' for
#<ActionView::Helpers::DateTimeSelector:0x7f556dbb6678>

Please help me

Aren't you using any kind of date_select plugin?