The unpack command should be just tar -xvf gpredict-x.y.z.tar.bz2 instead of the original.(z flag is used only for tar.gz files)
PFA the error image for the same, hope this helps!
on modern distros you can often get away with not specifying compression at all when extracting, xvf is then enough. I’d refrain from using sudo when it’s not needed as well.