thanks pechter!
Kies was the problem.
I followed the instructions in this thread http://forums.sandisk.com/t5/All-SanDisk-USB-Flash-Drives/sandisk-cruzer-blade-problem-troubleshooting-does-not-recognize/m-p/290781#M4216 and it cured the problem.
I should point out that it didn’t affect any other brand of flash drive that I tried, the incompatibility appears to be only between the Sandisk Cruzer and Kies, which leads me to conclude that it’s a Sandisk problem.
