Hal Gibson reports that on three different drives previously formatted with APS PowerTools, updating to 4.0.9 prevented the drive from mounting. Neither APS Mounter, nor Norton Utilities, nor any other SCSI Tool could get the drive to appear on the Desktop. APS told Hal to revert to 4.0.7, and reinstall drivers. Everything worked again.
No word yet as to how general this problem is.
Update: Bart Windrum has 4.0.9 running on his 660av with no problem at all. Several other readers are also reporting no problems. Based on another report from a reader who did have the problem, this may be another case where some users will have to reformat the drive, rather than just update the driver, before you can use the new version.