When the E18 error is present and that the lens system is out to the “off”, but retracts and go out with “on”, it acts can be of a blocked problem focussing.  
 
The following links is interesting for the Canon Ixus 750 or similar:  
http://tumbleweed.org.za/  
As it is known as: to check that the focussing system functions perfectly.  
 
The screw below A being difficult to turn to make move the lens of focus, it is enough to dismount the metal plate hiding the gears on the outlet side of the actuator of focus (metallic cylinder to the top of the red circle)  
 
and to make turn the gears on the outlet side of the actuator with a small screwdriver and go up the lens to half the height.  
Then, to make leave the objective (if it is in retracted position) while turning the large gears the zoom, released of the actuator for more facility,  
To connect the ribbon connectors of the ordering of the objective on the mother chart, to start, the apparatus posts E18 once again, to again restart, the lens of the focussing system finds its place, E18 disappears.  
As it is known as, it is not necessary to assemble for testing, the connection of the ribbon connectors of the lens system on the mother chart is enough.  
Thus I solved E18 on my Canon Ixus, after 3 dismantle / reassembly
Sorry, I am French and I do not speak very well English.

IWH dans ce trollpic de qualitay