When the first edition of the SnB books came out, there were a ton of errors. According to the SnB errata page for the Big Sack Sweater:
Big Sack Sweater: Under Front Neck Shaping: For sizes Small (Medium) only: BO1, ssk, BO this ssk by passing the st already on the RH needle over it, BO 0 (1) st
That may be what's causing you problems. If not, which portion of the pattern are you specifically having trouble with? I can grab my book and see if I can help you out.
Oh, and just for future reference...this is the SnB errata page (corrections for any incorrect patterns in all of the books):
Stitch 'n Bitch Errata