passwd utility - error .. not found

I’ve got problems using the passwd utility on my embedded system. Passwd utility only prompts the defined entries in the etc/passwd file and states “not found”. I don’t have the exact output by hand now but it is something like:
passwd1: root:x:0:0:superuser:/:bin/sh not found
passwd2: …(entry for second user defined in etc/passwd) not found

Beside etc/passwd I have also the etc/group and etc/shadow file so the account informations should be complete. There is no etc/.pwlock file.

Thanks for any piece of advice!

Is /bin/sh on your embedded system?