That is quite a jump in OS versions.
I have seen problems with other versions of Unix, Amdahl, where they don't like importing another /etc/passwd file from an older version of the OS. We recently did an upgrade and had similar problems, but much worse than yours. Users weren't able to login.
My experience is that it is some internal error. We had to rebuild the passwd files on each of 8 or so servers.
Couple of questions. Did you use /etc/shadow before? How did you append? Simply by ftp or rcp and >> passwd?
here is something I found on HP's website
www.itrc.hp.com
http://docs.hp.com/cgi-bin/fsearch/f...0020528-132922
You may have something different but similar to this. Hope it helps you out. Look at the return values down the page. You will see your exact error message.