You encountered the CalculiX limitations explained here: Utilities to handle ccx issues with shells in steady state dynamics
Workarounds are available (to get rid of the error, just export the .inp file, remove *BOUNDARY, OP=NEW from the second step and submit the analysis using standalone ccx solver) but it might be better to use solid (hexahedral) elements instead of shells in this case. Shells in CalculiX are expanded to solids anyway.