Must Declare Scalar Variable???

OK i have my stored procedure all set up and working.. But when i try and add a second variable called @iuser and then after i execute the stored procedure, i get an error saying:-
ERROR
"Must declare scalar variable @iuser"

Here is the code i am using in my stored proc, also my stored proc worked fine before i used a second variable??!

//BEGIN

ALTER PROCEDURE [dbo].[putpending]
(@cuuser nvarchar(1000), @iuser nvarchar(1000))

AS
Declare @sql nvarchar(1000)

SELECT @sql =
'INSERT INTO ' +
@cuuser +
' (Pending) VALUES (@iuser)'

EXECUTE (@sql)

RETURN
//END

And i know my VB.NET code is working but i will put it in anyway:-

//BEGIN

'variables
Dim user As String
user = Profile.UserName
Dim intenduser As String
intenduser = DetailsView1.Rows(0).Cells(1).Text.ToString()

'connection settings
Dim cs As String
cs = "Data Source=.SQLEXPRESS;AttachDbFilename=|DataDirectory|friends.mdf;Integrated Security=True;User Instance=True"
Dim scn As New SqlConnection(cs)
'parameters
Dim cmd As New SqlCommand("putpending", scn)
cmd.CommandType = CommandType.StoredProcedure
cmd.Parameters.Add("@cuuser", SqlDbType.NVarChar, 1000)
cmd.Parameters("@cuuser").Value = user
cmd.Parameters.Add("@iuser", SqlDbType.NVarChar, 1000)
cmd.Parameters("@iuser").Value = intenduser
'execute
scn.Open()

cmd.ExecuteNonQuery()

scn.Close()
//END

Any ideas why i am getting this error message?