I had this problem long ago with formulas.
Now I have it again with dates.
I'm assigning a date (or formula) to a cell, but Excel doesn't see it like date/formula. To make it work i have to enter the formula line and press Enter key. After that formula starts to calculate and date becomes a date value and I can formate it like "April, 2007" or 01.01.2007, etc.
I've tried to assign .Value property, to .Formula property
Nothing helps