Screen Sharing works sometimes

So I have an iPhone and iPad which I have installed a vnc application called Remoter on. The application is very straight forward and I have configured my router to forward VNC 5900 to my computer. Everyday I try it, it does not work. I hit connect and It basically just seems to time out. I go home, I check my router and sure enough the correct port is active. Then, I switch it to another port (5800), apply it, and then switch it back to 5900. I whip out the phone (over 3G) and push connect. It works without a problem. The next day, while I am out and about, I want to check something on my home computer so I try to connect with Remoter. The connection times out! What the **** is going on? Anyone have any idea.