Hi miroslavbucek,
I notice you have the Sony HDR-CX520. The issue explained in the following Apple article may solve your problem:
http://support.apple.com/kb/HT1793
Your camera is listed on Apple's Camcorder Support page here:
http://support.apple.com/kb/HT3290#2
The reference in the right hand column links to the above article.
If you have recorded any video in Standard Definition (MPEG-2), this MUST be erased from the camera before you are able to import High Definition (AVCHD) footage. Import the SD footage to iPhoto before erasing it from the camera - haven't tried this but I believe that's how it's done!
This information was mentioned by "envisioninc" in an earlier post in this topic.
Hope this helps!
John
Message was edited by: John Cogdell