Thank you for these hints.
Unfortunately nothing really worked.
In some cases it seemed to be not just long file+ pathnames, in some cases there were special charakters which windows did not accept.
As one example this "thing" was rejected
when being part of the pathname.
My "workaround":
I moved a backupcopy of my calibrelibrary to a network folder.
Inside a WindowsXP-virtual machine (running on ubuntu) i chose this library inside of calibre as active.
Then i moved it via calibre to the virtual NTFS-drive inside the machine.
So calibre aborted error on each book with unaccepted filepaths/names.
I removed these books from the library and moved the library without these books sucessfully to the virtual machine.
After shortening/correcting the paths and long filenames i manually added these books back to the library.
Til 2014 i have to watch the path/filenames and length for possible problems between ubuntu and winxp.
In 2014 the problem will be gone cause wife accepted to migrated her laptop to linux...

thanks god she hates Win8 gui.