The format for date entry must always be in the order of day-month-year. It is not necessary to key leading zeros. Any of the following characters may be used to separate the day, month and year:

•  . (period, full stop)
•  - (hyphen)
•  / (slash)
•  \ (backslash)

The year will always default to the current century, therefore if 1.1.90 is keyed as a patient's date of birth, the program will display 01.01.1990. Key 1890 for the previous century. So after 1999 most patient's dates of birth will need to be entered with a four-digit year.
If you get the message "Invalid date entry" check that you haven't used letters in place of numbers, i.e. O (upper case o) for 0 and 1 (lower case L) for l.