first - check fuse E6 to see if it's blown. Replace or swap in another just in case. There are some TSBs for this issue as it could be a couple of things - hose from fuel sending unit blocking flapper in filler neck, EVAP canister, or just the blown fuse. Lots of info in the archives. Solution might as simple as an "Italian tune-up" - ask me how I know
Here are a couple of threads to look at as well. If you're a contributing member to renntech.org, you can print a copy of the TSBs as there are 2-3 which apply to this issue.
HELP gas tank or gas pump problem?
http://www.renntech.org/forums/index.php?showtopic=5265
http://www.renntech.org/forums/index.php?showtopic=9358&hl=