convert(DATE,CONVERT(VARCHAR(10),@EnterStartYear) + '-' + CONVERT(VARCHAR(10),@EnterStartPeriod) + '-01') AS StartOfMonth,
  DATEADD(dd,-1,CONVERT(DATE,CONVERT(VARCHAR(10),@EnterStartYear) + '-' + CONVERT(VARCHAR(10),@EnterEndPeriod + 1) + '-01'))  AS LastOfMonth

The Above Code works in SSMS when i run with my query however when i am trying to add it to my Dataset, I am getting an error

"

Type DATE is not a defined system type"

However when i Change it to below code , SSRS accepts the code but I still get an error

convert(DATETIME,CONVERT(VARCHAR(10),@EnterStartYear) + '-' + CONVERT(VARCHAR(10),@EnterStartPeriod) + '-01') AS StartOfMonth,
  DATEADD(dd,-1,CONVERT(DATETIME,CONVERT(VARCHAR(10),@EnterStartYear) + '-' + CONVERT(VARCHAR(10),@EnterEndPeriod + 1) + '-01'))  AS LastOfMonth

Error: 

Cannot read the next data row for the Dataset1
The Conversion of a Char Data type to a Datetime Data type resulted in an 
out of range datetime value

Can someone help me out??

FM