Question concerning field updates using Date values

I am trying to do a field update in the action frame work with a Date field.  I would like to set a date field to be 2 months in the future.  I created an action - Update a field on row, select the date field to update, for Value select ‘Next n Days’ and enter 56 for the day value.  When the frame work runs it does not appear the date field gets set.   It does appear to work if I set the date field to a specific date.  Any suggestions?