The first time you tried to open the apps builder from the new pc, did it allow you to see the application you built, but when you tried to open the application it gave you the server not available error??
I have come across a possible similar problem... if i built the application from one pc, everytime i tried to open the application, i was able to do so and make changes etc.. if i tried to open the application from a different pc, i would get the error message you are receiveing. If i was then to return to the original pc, i would not be able to open the application and again receive the error message as before.
The way i found to stop this from happening, is load apps builder to one pc, and always use this connection to change any of the applications built. you will also probably need to rebuild the application you already have and give it a new id etc...
Sean.