Hi, thanks for your fast answer! Yes: 1) I can access windows normally (in fact, the files Ubuntu wrote, were on an NTFS boot partition, done by Windows XP) and all its files 2) I can access windows files from within ubuntu also perfectly 3) I can access all the files that I created/moved, etc. when using ubuntu 4) I CANNOT access SOME files in SOME folders, created/moved with Ubuntu, when I am in Windows. I see just the main folder that contains those files, and I cannot access the subfolders, and I also cannot access the "properties" feature of the folder (windows says just "access denied" or similar). Those files were originally windows files, but I moved them to other locations on the same disk. So they should have "windows compatible" names and characters in their names.
I am no specialist in Ubuntu (a total beginner in fact) but I could imagine that there are some issues with ntfs settings for those files (access permissions) for some mysterious reason.
I don't know if I told this before: I use a startup disk with Ubuntu 10.10. (wanted to install, but as I have these problems, I delayed the definitive installation on a separate disk partition)
Could it be that, perhaps, if Ubuntu does not exit/shutdown in a right way (this seems to happen sometimes), the just written files could get some problem with the access permission? (just an idea).