well... did u used the 6.35 PRO-A4 before use the PRO-B?
because if u did, u have to unninstal the previous CFW.
not just delete the 635PROUPDATE folder from PSP>GAME.
you have to load the updater on ur PSP and press the triangle button to unninstal the previous version (like 6.35 PRO-A4)
and only then u should try to instal the PRO-B.
I had the same problem on my Go, what I did is delete everything in my SEPLUGINS folder and then ran the installer and it worked perfectly. I think it has to do with the vsh and game files.