Calculate Time Difference between two dates and avoid exceptions

it is a coding on sql query where trying to get the average of time differences between 2 dates on 3 records. currently having error like : The datediff function resulted in an overflow. The number of dateparts separating two date/time instances is too large. Try to use datediff with a less precise datepart. when the first date is : 2012-04-20 00:00:00.000 and the 2nd date is : 1900-01-01 00:00:00.000 ## Deliverables * * *This broadcast message was sent to all bidders on Tuesday May 15, 2012 8:31:55 AM: it is SQL Server 2008 script