system out of memory exception in SSRS 2008 R2

Hi  All,

 Currently  i am  working in SSRS 2008 R2 in which i am using a stored procedure  as a query for generating a report which gives me more than 3 lakh records.execution of sp is fine ,but when i am using it in a report and  executing it after running for some time in BIDS  the report gives an error as  

Exception of type 'System.OutOfMemoryException' was thrown.

      I  have no idea about this exception. help me to get rid of this problem.

Thanks in advance,

Sanjay

sanjay