I notice that your message header indicates Office 2010 64 bit. I have no idea to what extent the 64 bit version will work correctly with DTPicker (if at all).
Did you set the initial value of the picker e.g.
Code:
Me.DTPicker1.Value = Date
There's an alternative picker available from Trevor Eyre that will work when DTPicker is a problem
You can find that here. Although intended for Excel, it needs only very minor mods to work in Word, and I use it in a couple of my own add-ins.