"msgstr" was expected but not found

As I export my language in Drupal 6 and try to import it, I get the following error:
The translation file fi.po (finnish) contains an error: "msgstr" was expected but not found on line xxx
The translation import of fi.po failed

I found a related problem here: http://drupal.org/node/253903

I added a plural header which is missing from my po-file and to deleted all lines related to plurals. This way I managed to import the file, but when I export it, the plural header is missing again.

Any solutions?

Tnks in advance!