This can happen if you leave the filament inside the extruder for a long period of time or shut down the printer before the nozzle is cooled down.

Preheat the nozzle to a high temperature so the filament melts down. Go to settings and change the temperature to about 240-250 degrees, preheat the nozzle.

Go back to menu and unload the filament. Sometimes you need force the filament out from the nozzle.

Cut the edge on the filament and load again. You might need to push the filament thought the nozzle.

Yes, you can use any PLA filament that is 1.75mm thick. But the size of the Panospace roll is made to fit in to the printer so in that case you need to feed the filament separate from the printer.
We do recommend that you use the Panospace filament because it has been tested together with the printer.

On the left side when you look at the front of the 3D printer

After you sliced a model in Panobuilder you will see how many grams you model will weigh. On the side of the filament roll, you will see how many grams are left on the roll.