SQL Server Datediff vs SSRS Expression DateDiff function

ENVIRONMENT: SQL SERVER 2005, SSRS 2005

Help understanding inconsistent results between sql server and ssrs?

I am using the below function to calculate number of days in SQL:

select datediff(d, '2013-04-19 09:36:00.000','2013-05-24 08:36:00.000')

I get an output of 35

When I use the below statement in SSRS
DateDiff(DateInterval.Day
, “2013-04-19 09:36:00.000”,”2013-05-24 08:36:00.000”)

I get 34 as my output.

Could some one please educate me regarding this difference as I have
now hit a big thick brick wall and cannot understand why this is
happening?

Thanks all for your time.