problem with maskeditextender

Hi , my problem is as follows: I have a asp.net web form with a textbox and a maskeditextender. The mask contains a period (.) and this works perfectly on the machine it was developed on , however ive just moved over to a new laptop and now using the exact same source every time i debug the period turns to a comma (,) and this means the text in the textbox is no longer accepted as a floating point value.

How is this possible?

<asp:MaskedEditExtender ID="TextBox4_MaskedEditExtender" runat="server" Mask="99.999"
                MaskType="Number" TargetControlID="TextBox4"></asp:MaskedEditExtender>