From Lotus Knowledegbase article # 151467

When the date format is wrong on the Domino console and text dates created by agents running on that server and the server is running on Windows NT as a service, this is due to the system locale being wrong (normally US) :

HKUSERS\.default\control panel\International\dDate is the separator character for dates

HKUSERS\.default\control panel\International\iDate is the date format:

0=m/d/yy (US)
1=d/m/yy (UK)
2=yy/m/d (Japanese)

Restart the Domino service and the change will be picked up. Other time & date entries are under the same key.

(See file: Notes_Server_Date_Format.reg to set NT default locale to UK settings)

You should first check the regional settings control panel and use the "set default" button to reset the default locale settings having also change the current logged in user settings.  If Domino runs as a specific users account it is easiest to login interactively as that user and amend the settings in the control panel.  If this is not possible due to restricted interactive login rights then find the relevant profile under HKUSERS and amend the iDate, dDate, sShortDate, and sLongDate fields (amongst others) in the above International keys to be the correct date format.

This is typically noticed in a Notes application with a scheduled agent that uses LotusScript commands such as "Now" etc. to get the current time for stamping on a document as the "last updated" time as the "last updated" time will stamp an incorrect date on from 1st to 12th each month and most likely fail for the rest.

The Notes log database and the domino console may or not record the incorrect date format.