UMAX Astra 4000U "Scanner Not Found" error: the solution

A reader writes: "When installed according to the instructions provided, the new UMAX Astra 4000U Scanner gives a "scanner not found" error (Driver 17) on the Mac with the green LED on the scanner flashing error code 71.

The problem is that there is an undocumented mechanical scanner lock which is shipped locked, preventing the scanner's power-up sequence. Lift up and remove the scanner's paper cover and flip (rotate) the plastic switch hidden under the orange hinge from the locked icon to the unlocked icon positions. Then unplug and replug the scanner power. Problem fixed."

[Note: I just got an Agfa SnapScan scanner. It has a similar lock. But it is clearly indicated in the documentation that you need to unlock it before you use the scanner.]