Ah, I think I see the issue here, and it has to do with an assumption being made that the first line is a undeclared header, which in your case is wrong.  Can you trying adding to your set_meta:

and then restart your sever and then create a new dataset with your tool?

OK, got it to work. Guess I combined both of your suggestions in a way. It ended up looking like this:

    def set_meta( self, dataset, overwrite = True, skip = None, max_data_lines = None, max_guess_type_data_lines = None, **kwd ):

        dataset.metadata.columns = 5

        dataset.metadata.column_types = ['str','str','int','str','int']

It might have worked after all in one of the previous attempts but I did not create a new dataset. I did like you suggested and now it works.

Thanks a lot, you saved my day !

Regards,

Marc