Using SSRS, Report Builder 3.0, MSSQL 2008 and query to an Oracle 11G database, I found that the oracle stored procedure ran well, produced consistent results with no errors. When I tried bringing the data into SSRS, I got the error as listed in OP's query. I found that the data loaded and displayed only if I removed the parameters (not a good idea). On Further examination, I found that under dataset properties>parameters I had set the start date to parameterName P_Start and parameter Value to @P_Start.
Adding the Parameter value as [@P_Start] cleared the problem, and the data loads well, with parameters in place.