If I try to "move to another package" a class I always get an exception.

Yes me too and I added a bug entry. Thanks for reporting and we should fix that.

Try moving any class present in the standard Pharo 3 to AST-Core, for example...

Anyway, thanks for the great work you are doing.

Tx Remember Pharo is yours and you can get an impact :) and have a lot of fun.

Regards

José