Created attachment 2715 [details]
patch

In the Simulator::Schedule implementations there are two checks:

  Time tAbsolute = delay + TimeStep (m_currentTs);
  NS_ASSERT (tAbsolute.IsPositive ());
  NS_ASSERT (tAbsolute >= TimeStep (m_currentTs));

Since m_currentTs is always positive, one is redundant.
It is enough to check that delay is positive.

Moreover, adding a more explicit error message is needed.