Thank you for your answer. I did that, I also deleted the whole configuration folder but it didn´t help. It is weird... DW remembers some sites info, but not all.
For this particular site, I have used the Incontext editing and that has also caused some problems: A client tried to edit the page and message poped up, The operation could not be performed because there is insufficient disk space or the file write permission is not granted. Next time it said: You cannot edit or duplicate this page, the page does not appear to contain any editable regions. When I went to the page, it said that the page doctype is not valid...
And there is disk space, editable reagions and the page doctype is transitional 4. 01... I don´t know if this has something to do with this site info problem, but I guess that is another issue.
Any more ideas?
It didn´t have anything to do with the Incontext editor... It looses every site info exept the ones I created a week ago, (I imported two sites from the web).