ADO.NET Stored procedure won't INSERT Binary data

Okay, basically I have a stored procedure that doesn't seem to work.  The SP should insert a new row (updating a username and data column) into the DB and return an identity value.  Well, it inserts the username okay, returns the unique identifier, but never sets the @data passed to it.  The column type is Binary, size 4096, I am passing it a (c#) SqlBinary of the same size.

Looked at the SqlCommand right before I execute, the parameters look fine.  Any ideas?


Here is my SP:

CREATE PROCEDURE dbo.sp_InsertStuff
     @user AS VARCHAR(4),
     @data AS BINARY
AS

INSERT INTO UserStuff (UserId, Data)
VALUES (@user , @data)

RETURN @@identity
GO


Here is the C# code:

//stuff does not exist, call stored procedure to insert it
SqlCommand cmd = new SqlCommand("sp_InsertStuff", sqlConn);
cmd.CommandType = CommandType.StoredProcedure;

//set up the parameters
SqlParameter parm = cmd.Parameters.Add("RETVAL", SqlDbType.Int);
parm.Direction = ParameterDirection.ReturnValue;
cmd.Parameters.Add("@user", SqlDbType.VarChar).Value = sUser;          
cmd.Parameters.Add("@data", tb.data);
// tried this instead, didn't help
//SqlParameter binaryShit = new SqlParameter("@data", tb.data);
//cmd.Parameters.Add(binaryShit);
         
//execute the stored procedure and return the stuff id
sqlConn.Open();
//note that the data in the third parameter of cmd looks fine here
cmd.ExecuteNonQuery();
//no exception is thrown, record inserted into DB, but nothing in the data column
sqlConn.Close();
return (int)cmd.Parameters["RETVAL"].Value;