galaxy tab and sipdroid

Hi, I was hoping someone here could help a droid novice out. I bought a gt-p1000 and installed sipdroid. I also registered with pbxes.org. When I try to make a call with sipdroid the screen has the appearance of connecting and ending the call then the entire program vanishes from my screen. Please excuse my naivety, but am I missing a step in setting up this droid to do voip calls?

Thanks, any help at all would be appreciated.
Bernie