How is your 'uc' variable declared because this:
vb.net Code:
  1. tp.Controls(0)
will only return a Control reference. If you've declared 'uc' as type Control then you won't get Intellisense because the Control class doesn't have a TextProperty property. If you have declared 'uc' as the correct type then you must have Option Strict turned Off or this:
vb.net Code:
  1. uc = tp.Controls(0)
wouldn't compile.

I'd rather see safer code like this:
vb.net Code:
  1. For Each page As TabPage In Me.tbcTasks.TabPages
  2.     For Each ctl As Control In page.Controls
  3.         If TypeOf ctl Is MyUserControl Then
  4.             MessageBox.Show(DirectCast(ctl, MyUserControl).TextProperty)
  5.             Exit For
  6.         End If
  7.     Next ctl
  8. Next page