Opened mine today due to same symptom. It is not due to any physical obstruction.
To Open: Remove top cover.
Remove 4 screws from bottom
Start by prying along middle of rear edge. There is a catch at this point, so the top must be pried away from the bottom as the bottom is pushed in slightly. Once slighly open I stuffed in a small rag to keep them from snapping closed again.
Similar catches are found in the middle of each side.
The front has 2 double catches about 1 to 2 inches in from the corners. These are especially stiff, but once the sides and rear are open, it is just a matter of pushing the top piece from the rear, to free them.
There is one white connector to the pushbutton printed circuit board that may be removed to free the top entirely.
If you find the cause, let us know. I think it is software or electronics related. The carriage moves freely, and if pushed away from the stop position, returns easily when a scan is tried. But the forward motion of the scan only advances an inch or so and returns with the dialog box about not unlocking the lock.
curt
Curt, January 2006
