Content from D6 to D7 is not imported

same effects here. For each node to be imported I get messages like

Warning: Invalid argument supplied for foreach() in node_export_file_field_import() (line 1091 in sites/all/modules/node_export/node_export.module).
Notice: Undefined index: auth_category in biblio_contextObject() (line 142 in sites/all/modules/biblio/includes/biblio.util.inc).

The content to import is of type "biblio". Most fields look ok, but the biblio-authors are not migrated. These entries should be inserted into table biblio_contributor, but no record can be found there.

EDIT:
Ok, the ERROR situation "Undefined index: auth_category" is solved, when changing line 142 from
$author = $node->biblio_contributors[$i]
to
$author = $node->biblio_contributors[$i][0]

But I am sure that this is a hack!
Another point is, that only the author-categories of type 1 (Author) is handled
if ($author['auth_category'] == 1)
But in my case all entries to be imported are of type 5 (Corporate Author). This might be the reason why no one author is migrated.

Using this module for migration across Drupal versions is not easy. You have to use Node Export Feeds which is a very manual process, or convert the D6 site to a D7 site first.