Q1. Below is code for the click events of your previous and next buttons. In the attached I've also made a few other changes to your code.
Q2. I'd take a guess the form is not showing because the user at the other end has not enabled macros when the warning pops up. If they don't see a warning then there is potentially something wrong with their Excel install.
As for the calendar not showing, that will all depend on which version of Excel they're using and whether or not they have the same calendar as you installed on their machine. Why not just let them enter a date manually rather than use the date picker? You can use validation to force the users to enter actual dates if that's what you're worried about.
BSB
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