No, it was an "allow access" permission. In my case the lack of permission was caused by https://bugs.launchpad.net/ubuntu/+source/consolekit/+bug/221844
I sort-of managed to reproduce the bug today on a not-too-out-of-date hardy system. I did the following:
1) Open System -> Administration -> Authorizations, set the "mount removable storage" permission for the active session to "No"
2) plug in pendrive
3) note that icon is not created on desktop (which is a plus, in the original bug it was created), but an entry shows up in the "Places" menu with "Mount .... pendrive" tooltip.
4) clicking on that entry in the "Places" menu has no effect.
So, apparently the bug is half gone: an icon is not added to the desktop, but the other half still remains: I assume that the entry in the places menu could be used for mounting it, and that clicking on in launches the mount operation, which silently fails.