cet-is » art » art_root_io

I am having an intermittent problem with the processing of some art root files in Mu2e. For these files, a data product was created and put in the art::Event.
The data product was never written out but its descendants are still present in the file. Since we do not need the original data product anymore, it was removed from the code base.

For some files in the dataset (and only for some of them, all the files in the dataset are produced in the exact same way) I get this error:

mu2e -c Print/fcl/fileDumper.fcl /pnfs/mu2e/tape/phy-sim/sim/mu2e/cosmic-g4s1s2-cry2general-cat/190320/art/b3/d1/sim.mu2e.cosmic-g4s1s2-cry2general-cat.190320.002705_00007035.art

cet::exception caught in art
---- DictionaryNotFound BEGIN
 No dictionary found for the following classes:
      art::Wrapper<vector<vector<mu2e::GenParticle> > >
      vector<vector<mu2e::GenParticle> >
 Most likely they were never generated, but it may be that they were generated in the wrong package.
 Please add (or move) the specification
      <class name="MyClassName"/>
 to the appropriate classes_def.xml file.
 Also, if this class has any transient members,
 you need to specify them in classes_def.xml.
---- DictionaryNotFound END
%MSG
Art has completed and will exit with status 7.

The error does not appear with e.g. /pnfs/mu2e/tape/phy-sim/sim/mu2e/cosmic-g4s1s2-cry2general-cat/190320/art/b3/d1/sim.mu2e.cosmic-g4s1s2-cry2general-cat.190320.002705_00007035.art

Putting the schema back fixes the issue but it would be interesting to understand why this error happens only for some files.