Calendar dates not showing

I have created a pop up <nobr>calendar</nobr> on a user form in Excel 2007 using Calendar Control 12.0. I created it with a blue background and black digits.

Someone else used the form and when the calendar popped up, the month and year were correct at the top but the calendar had a white background with a dash where the numbers should be in the date squares on the grid. If you click on a date square, the date will appear correctly.

The other user is also using Excel 2007 but has calendar control 8.0. This form has to be used by several users in the office and I would like to know what is actually causing the calendar to not appear correctly and what can be done to rectify this.

Thanks