It's a Leap Year, have you changed your Financial Year dates?
To avoid conflict at the end of the month, it's important you change the end date of February to prevent any errors on the 29th!
See below...
Go to Company menu, choose "More Options" and select “Financial Year”- where February end date is you will need to change this to 29/02.
Please be aware of this setting if you're running a Year End before 2024. Make sure to temporarily set it to 28, and then revert it back after completing Year End.
If this is not carried out, an error message will appear, ‘Invalid Argument to Date Error’ when adding any order. You may also see ‘Out of Posting Period’ prompting when in Xline.