Ubuntu Guide posted a tutorial about fixing the left click after upgrading to Ubuntu 10.10 Maverick

If your mouse's left click stopped working after upgrading to Ubuntu 10.10 Maverick, but it was working well on the old Ubuntu. You can try following method to fix the problem. Download an appropriate xsever-xorg-input-uvdev package with the bug fixed from this page. Then double click to install, and finally log-out and back in.

  Fix Left Click not working after upgrading to Ubuntu 10.10 Maverick