Sunbird: importing calenders

I tried to import my old calenders and a new "professional" one with bank holidays.
With one calender I succeeded but with all the others I get this
http://avogadro.techfak.uni-bielefeld.de/~ipo/sunbird.import.error.jpg
error message.
I can import the calender files in the non-portable version.
Does anybody know?
Thanks,
I.