Adjust the Date range to be less than 12 months on the General tab.  

The Consecutive Years Report can only be run for a maximum of 12 month periods.  While the report can be run for consecutive years for part of the year (such as 3 months), it cannot be run for a date range of 16 months (e.g., 1/1/2009-4/30/2010).  To find the constituents who gave in longer intervals, users will need to create a query on donors who have given in consecutive time periods.