I dont know this is any help but check your regional settings on the control panel.
To stop a field from being editable, set the Locked setting to Yes in data tab of the fields Property. If use this method u wont be able able to add data. If u wanted to add data and lock it soon after, it will require some minor coding. e.g
In the after Update of the field add this. change the my control names to suit the name of your controls. This will lock the field after a value has been entered. You need someway of unlocking if u need to make any changes.
If Me.YourTextboxName.Value Then
Me.YourTextBoxName.Locked = True
Me.YourTextBoxName.Locked = False
In the OnCurrent of the form
If IsNull(Me.YourControlName) Then
Me.YourControlName.Locked = False
Me.YourControlName.Locked = True
See how ya go with these,. These are only suggestion. others may have a better way of doing it. This will at least point you in the reight direction.