You must create a new SqlParameter for each Parameter, it should be like this:
using (SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["intranetv2"].ConnectionString))
{
SqlCommand cmd = new SqlCommand("insert into [MyBase].[Dbo].[LogErrors] (Username, StackTrace, ShortDescription, DetailDescription, ErrorType) VALUES (@Login, @Stack, @Message, @Txt, @Source)", conn);
SqlParameter param = new SqlParameter();
param.ParameterName = "@Login";
param.Value = user.Login;
cmd.Parameters.Add(param);
SqlParameter param2 = new SqlParameter();
param2.ParameterName = "@Stack";
param2.Value = ex.StackTrace;
cmd.Parameters.Add(param2);
(...)