Thanks for the bug report I found the bug in DBForums.cs:
public static bool UpdateUserStats(int userId)
SqlParameterHelper sph = new SqlParameterHelper(GetConnectionString(), "mp_Forums_UpdateUserStats", 1);
sph.DefineSqlParameter("UserID", SqlDbType.Int, ParameterDirection.Input, userId);
int rowsAffected = sph.ExecuteNonQuery();
return (rowsAffected > -1);
as you said it was missing the @ for the parameter. I've fixed it here.
I need to look at that redirect when deleting a thread, it seems because the thread no longer exists it results in the access denied page. Need to do something more graceful there.