  We analyse high-resolution Hubble Space Telescope/Advanced Camera for Surveys
imaging of the nuclear starburst region of M82, obtained as part of the Hubble
Heritage mosaic made of this galaxy, in four filters (Johnson-Cousins
equivalent B, V, and I broad bands, and an Halpha narrow-band filter), as well
as subsequently acquired U-band images. We find a complex system of ~150 star
clusters in the inner few 100 pc of the galaxy. We do not find any conclusive
evidence of a cluster-formation epoch associated with the most recent starburst
event, believed to have occurred about 4-6 Myr ago. This apparent evidence of
decoupling between cluster and field-star formation is consistent with the view
that star cluster formation requires special conditions. However, we strongly
caution, and provide compelling evidence, that the `standard' simple stellar
population analysis method we have used significantly underestimates the true
uncertainties in the derived ages due to stochasticity in the stellar initial
mass function and the corresponding sampling effects.
