Ubuntu doesn't recognise my password after upgrading from 11.04 to 11.10
I am a new user and had been using Ubuntu successfully on my Dell Inspiron 1525 for one week, until I was prompted to upgrade to 11.10. At first the upgrade seemed to have been successful, but I followed some advice to change my password to make it stronger. Since then I have been unable to log in to my user account using the new password (or the old one!).
Following advice on other similar threads I have opened the recovery console and dropped to root shell prompt.
I was unable to change the password again with "passwd username", receiving the message "Authentication token manipulation error".
I was also unable to delete the new password with "passwd -d", receiving the message "cannot lock /etc/shadow; try again later.".
Using the command "ls /etc" I cannot see any files with the suffix ".lock", and trying "rm etc/shadow.lock" brings up "cannot remove 'etc/shadow.lock': No such file or directory". There do appear to be files such as shadow-, group-, gshadow- and passwd-, as well as the same file names but without the trailing hyphen.
Any ideas on what I should try next? Apologies if it's obvious, but I am very new to Ubuntu.