some problems with groupby

Hi!, i'm trying to make a "easy" test on knime, so i have to remove duplicate rows in a table from a file.

Well, i could do this with a groupby node, then a row filter node and at last a reference filter node, and this works for two of the three file that i have to read...

When i loadded the last one and i connected it to the groupby, it shown me an alert, but when i excecute it it simply runs but it doesn't add the count column that i added in "Type based aggregation" (the other two, yes)

Do you have some idea about what is wrong?

duplicate thread see answers here: