ssrs 2008 report not working when use a stored procedure

In a new SSRS 2008 report, I am going to change the inline sql to a stored
procedure since that is a requiement for the project I am working on. The sql works fine within the ssrs 2008 report, but
has a problem in the stored procedure.

The error message that is displayed  is the following:
'Query execution failed for dataset Msg 8114, Level 16, State 1 Procedure spRec,
line 0 Error converting data type varchar to int.' 
The stored procedure works if I select only 1 report. However if I select 2 or more reports that is when the above error occurs.

The ssrs 2008 report has 18 embedded tablixes within the main tablix. The
embedded tablixes wiithin the ssrs main tablix will display selected reports based upon a report parameter that a user.
The embedded reports will be displayed based upon the report number. In addition, I only want the data for
the selected reports to be returned from the sql. I want this to occur since the data from the runs will be more than is
needed for each uniuqe run. Note: The data returned will be all in the same format. There will be a column in each
data row showing what report number the data should be selected for.

The report parameter is setup as allow multiple values and data type = text.
The dataset to pass data to the report parameter looks like:
SELECT 'Locator' AS rptName, 1 AS rptValue
      UNION
SELECT 'letter',2
      UNION
SELECT 'Wallet ',  3
     UNION
SELECT 'Cum Stu', 4
     UNION
SELECT 'Attend', 5
    UNION
SELECT  'Test',6

The sql before each section looks like:

IF 1 in (@report)

IF 2 in (@report)

I have tried changing the properties of the report parameter to integer and the
if statements listed above but it has not worked.

Thus can you tell me what I can do to solve my problem?