Lens error is displayed on nikon coolpix L 4. what do I do?

Here are a few possible fixes :
Fix #1: Remove the batteries from the camera, wait a few minutes. Put a fresh set of batteries back in (preferably rechargeable NiMH 2500mah or better) and turn the camera on. If that didn't work, try pressing and holding the Function or OK button while turning the camera on.
Fix #2: If the camera's batteries ran down completely while the its lens was still open, the camera may show a lens error or not start properly when new batteries are installed. Remove the memory card and keep it removed, then install the new batteries. When you turn the camera on with the card removed it may come back to life, as this triggers a reset in some cameras. Error E30 (for older Canon's) means that you don't have a memory card installed, so turn it off, slip in the SD card and turn it on one last time

Fix #3: Insert the cameras Audio/Video (AV) cable, and turn the camera on. Inserting this cable ensures that the camera's LCD screen remains off during the start process. Thus extra battery power is available to the camera's lens motor during startup. This extra power can be useful in overcoming grit or sand particals that may be jamming the lens. If the AV cable doesn't fix the lens error by itself, consider keeping this cable installed while trying fixes 4, 5, and 7 as a means to provide extra power to help to these fixes. But note that I DON'T recommend keeping the cable installed during Fix 6 as you may damage the AV port while tapping the camera. Reinsert the cable only AFTER tapping the camera.

Fix #4: Place the camera flat on its back on a table, pointed at the ceiling. Press and hold the shutter button down, and at the same time press the power-on button. The idea is that the camera will try to autofocus while the lens is extending, hopefully seating the lens barrel guide pins back into their slots.

Fix #5: Blow compressed air in the gaps around the lens barrels with the idea of blowing out any sand or grit that may be in there jamming the lens. Other variations include blowing with a hair dryer in “no heat” setting, or sucking the gaps with a vacuum (careful with this one). Some people also have actually used a "Shop Vac" with this fix to help extend a retracted lens.