Investigate and fix cryptic error message

Running DonadelliGruningHitaemann.mod in Dynare results in

terminate called after throwing an instance of 'SymbolTable::NoTypeSpecificIDException'

The problem seems to be due to there being 82 equations but 84 defined variables. After all, there is

WARNING: 'ni' not used in model block, removed by nostrict command-line option
WARNING: 'n' not used in model block, removed by nostrict command-line option

Deleting the two declared variables solves the issue.