I have written the following SP

I am trying to return a concatanated string

ALTER PROCEDURE usp_checkuser 

            @StrAppdi nvarchar(50)

AS


DECLARE @string nvarchar(4000)
SET @string = ''

SELECT @string = @string + CHAR(13) + dbo.DataClass.DataClassDesc
FROM  dbo.SysDataClass INNER JOIN
      dbo.DataClass ON dbo.SysDataClass.DataClassID = dbo.DataClass.DataClassID
WHERE (dbo.SysDataClass.SystemID = @StrAppdi)
ORDER BY dbo.SysDataClass.SystemID

print @string

RETURN @string

GO

declare @myret nvarchar

exec usp_checkuser '421' @myret

But I get these resuts in QA

Name
Car Registration
Travel Details
Server: Msg 245, Level 16, State 1, Procedure usp_checkuser, Line 19
Syntax error converting the nvarchar value '
Name
Car Registration

For some reason it is trying to deliver my results as an integer and falling over. What exec staement do I need to create a meaningful output. I am hoping to to call the returned concatenated string from a .net sqlcommand.

Many Thanks