Truncated OUTPUT Stored Procedure Values

Hi,

I created the SQL 2005 stored procedure below:

CREATE PROCEDURE [dbo].[STP_val_deliverable_path]
@s_no smallint,
@deliverable_path nvarchar(255) OUTPUT

When I run in ASP.NET 2005 the stored procedure from server explorer I
get the value 'X:my directory.......'.

When I run the procedure from code:

   Dim var_deliverable_path As String

       Dim cmm_select As New SqlCommand("STP_val_deliverable_path",
connection)
       cmm_select.CommandType = Data.CommandType.StoredProcedure

       var_param = New SqlParameter
       var_param.ParameterName = "deliverable_path"
       var_param.Direction = Data.ParameterDirection.Output
       var_param.Value = "C:"
       cmm_select.Parameters.Add(var_param)

       cmm_select.Connection.Open()

       cmm_select.ExecuteNonQuery()

       cmm_select.Connection.Close()

       var_deliverable_path =
CType(cmm_select.Parameters("deliverable_path").Value, String)

The var_deliverable_path has the value of 'X' only, not the whole
string.

What could be the problem ?