How to pass multi-valued characters in SSRS Report?
I found a solution. I did not properly split the values in the stored procedure with a UDF.

To pass multi-values correctly in this stored procedure, I would need to add the following code to the dataset parameter that I am using:

=join(Parameters!&lt;your param name&gt;.Value,",")


This is basically going to join multiple values into an array and pass it through the @Flag parameter. The next step is adding SQL to the stored procedure to receive and digest the values correctly so it reads the values with the IN clause.

Google search any UDF string parser online. There are many to choose from. I used dba_parseString_udf from Michelle Ufford http://sqlfool.com.

Once I had my UDF installed, I can now alter my IN clause to receive the new multi-valued parameter being passed by SSRS as follows:

WHERE [Flag] IN (SELECT * FROM dba_parseString_udf(@Flag, ','))


Therefore, SSRS will pass the following value:

@Flag = 'A,B,C'


Then my UDF will parse that string out correctly to:

A
B
C


And populate my @Flag parameter correctly with SELECT * FROM UDF()...