  Recently the HADES collaboration has published the invariant mass spectrum of
$e^+e^-$ pairs, dN/dM$_{e^+e^-}$, produced in C+C collisions at 2 AGeV. Using
electromagnetic probes, one hopes to get in this experiment information on
hadron properties at high density and temperature. Simulations show that firm
conclusions on possible in-medium modifications of meson properties will only
be possible when the elementary meson production cross sections, especially in
the pn channel, as well as production cross sections of baryonic resonances are
better known. Presently one can conclude that a) simulations overpredict by far
the cross section at $M_{e^+e^-} \approx M_{\omega}{^0}$ if free production
cross sections are used and that b) the upper limit of the $\eta$ decay into
$e^+e^-$ is smaller than the present upper limit of the Particle Data Group.
This is the result of simulations using the Isospin Quantum Molecular Dynamics
(IQMD) approach.
