user account locked up frequently

There is a user who is companing that his AD user account is getting locked up frequently. Can anyone tell me how to troubleshoot the problem? I think that he might have changed his passoword and some software is still using the old one. Any help would be appreciated.

You can try to enable the Auditing for logons: "Audit account logon events" and "Audit logon events". It could be possible that you can find some extra informations, you also need to check all DCs for the events. But normally no software uses the account from users.

You can even try to find it using Account Lockout and Management Tools from Microsoft and see if that works.

Can you tell us whether the account is logged into more than one machine or is it running a service on the same machine? A user might have mapped drives to a resource from one machine, on a different machine if he changes his password and then the first machine tries to stay mapped to a drive and the password is not correct and eventually locks the user out. So, to track down where the account is getting locked out, you can use eventcombMT.exe from the Account Lockout Tools that can be found on Microsoft website.