I had the same problem and unfortunately the 'read me' files don't adequately explain the process and
are somewhat misleading.
Felix said that the SV Builder doesn't generate the gallery, only configures it, therefore the gallery first needs to be generated from the standard SimpleViewer 2 files that should already be installed in the photoshop scripts file.
First, create standard gallery- go to menu in photoshop > file > show all items > scripts > simpleViewer_2 and create gallery. The output gallery that is generated from your images is where you need to replace the simpleviewer.swf file with the new .swf file from the web folder in the pro version. Then open this output gallery with SV Builder Pro which should then re-configure your settings to the pro settings.