Problem solved.
Hello, Nokia software developers! Have you just graduated from the kindergarden? Or, may be, developers of Flash utility for Windows are still there?
So, when I got my Nokia 770, I started to play with some software. Installed some applications, new themes and etc. I was not playing with system things. However something went wrong. I was not able to get rid of one theme and etc.
Even worse. I could not refresh list of packages in AM. I reflashed OS with the same version and had the same error with AM. I could not use application manager to connect to repository's and install new software. I started to worry, asked questions here, tried a couple of things and with your help learned something about my Nokia. Finally, I installed OS2007_hackers_edition. And with OS2007_HE everything worked fine. Then I reflashed back to original OS and magic happened-my Nokia started to work as expected. This means that by flashing with OS2007_HE something was rewritten. And OS2006 was not completely cleaning memory while reflashing.
Thank you all for your help. And, should we expect that commercial software for commercial product would work properly? This small things are making
very bad impression of really great product. I love my Nokia 770.