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.

For A4Tech mouse with the problem,see this solution :

Some solution, that solve our problem.
1) xinput –list
It will show you your input devices, our A4Tech mouse have id, for example, there are
⎜ ↳ A4TECH USB Device id=11 [slave pointer (2)]
⎜ ↳ A4TECH USB Device id=10 [slave pointer (2)]
2) xinput set-int-prop %id% “Device Enabled” 8 0
, where %id% is one of id’s of your mouse. In my case it was 10. Generally, this is the second id of list. This command will disable advanced built-in keyboard of A4Tech mouse.
If you want to enable back, use
xinput set-int-prop %id% “Device Enabled” 8 1.

Check here