If you deleted cods or shrunk the os you may have removed something that is needed.. I would go to docs to go site and redownload the app or reinstall it through the pc...
Same exact problem here. Looks like the BB-offered upgrade to 4.5.0.175 manages to break Sheet-To-Go. Oddly, the other two Documents To Go pieces (Word To Go and Slideshow To Go) still work fine.
And yes, I brilliantly upgraded myself into the chirp too (d-oh!).