The user account has been automatically locked

I am having  problems with user accounts locking and un lock  automatically

I had a look in the event viewer and it comes up with this error :

Event ID: 40690
>>> Type: Warning
>>> Usre: N/A
>>> Source: LSASRV
>>> Category: SPNEGO (Negotiator)
>>>
>>> Description:
>>> The Security System detected an attempted downgrade attack for
>>> cifs/LHFILE2.xmcht.nhs.uk. The failure code from
>>> authentication protocol Kerberos was "The user account has been
>>> automatically locked because too many invalid logon attempts or
>>> password change attempts have been requested.
>>> (0xc0000234)".