Fluid level is low... If it's low, there's not enough for the filter's pickup tube to grab the fluid for the trans pump and build pressure. Quick test, get the car up on jack stands at all four corners evenly. In the middle of the transmission pan there is a 17 or 19 mm bolt. In the middle of the bolt is a torx. It's a 30 if I remember correctly. Anyways, with the engine running, remove that center torx bolt. There should be a dribble of fluid coming out. If not, my low fluid comment stands.


If it's been parked for two years, I'd drain whatever fluid is in there, drop the pan and replace the filter, then refill the transmission to spec. When you drop the pan, be careful, there is about a quart still in it since the drain plug sits up above the floor of the pan. And before you complain about how there's no dipstick to check the level or to refill the tranny and Ford this and Ford that...realize that most manufacturers are going this route. It's not just a Ford thing.

Oh, refill capacity if you just do a pan drop, filter replace, and refil is about 6-6.5 quarts. You will want 7 quarts to be safe.

 

What he said but I'd also add that if the tranny fluid level is indeed low, you should be asking yourself why.
The chances are that there's a fluid leak somewhere and in cars that spend months sitting idle, it's probably from a degraded gasket. The most common is the tranny fluid pan gasket and you're going to replace that anyway if you're doing a fluid/filter change. The extension housing gasket is another common leak area so you might want to check that too.

 

tru dat. Fluid doesn't just evaporate.

Since it's not the easiest thing to top off the fluid, it's best to address the leak first, then drain/refill if it's not the pan gasket.