The problem could be dirt, debris or a dislodged lens. [http://camerarepair.blogspot.com/2007/12/fixing-lens-error-on-digital-camera.html|Here is] a great site that may help you getting it cleaned and working again. Of course there is also the possibility that you truly have a lens error.
"ZOOM LENS
ERROR
Movement of the lens barrel does not end within the specified time.
Cause and Probable Faulty Part:
MAIN PCB ASSm'Y
OPTICAL UNIT"
Now if you are inclined to fixing your camera, you can download the service manual [http://www.keepandshare.com/doc/3161702/canon-powershot-sd750-sd1000-digital-elph-digital-ixus-75-70-et-pdf-september-25-2011-8-35-pm?da=y|from here] or use the guides from here http://www.ifixit.com/Device/Canon_PowerShot_SD750#deviceGuides Good Luck.