Group asset of type {0} at position {1:N0} does not contain a similar value for all articles.
Explantion:
Certain fields may apply to a group of articles. When you change/add such a field, you must include all the articles in the group in question in the import file. You can recognise these fields in the file by the indication of "Group...".
Make sure that the GroupImage1...X, GroupIcon1...X, GroupUrl1...X and GroupDocument1...X fields are filled in the same, and in the same order for all articles in the group concerned. Then import again.