I experienced this problem after upgrade to Precise.
Gerry's suggestion ["System Settings" -> "Keyboard" -> "Shortcuts" -> "Navigation": "Switch Applications" ] indicated no binding for me. I set it to Alt-Tab and that solved the problem for me.
The general proble seems to be that that particular key binding [and I believe any others in that Navigation group) were wiped out or not properly migrated on upgrade.
I experienced this problem after upgrade to Precise.
Gerry's suggestion ["System Settings" -> "Keyboard" -> "Shortcuts" -> "Navigation": "Switch Applications" ] indicated no binding for me. I set it to Alt-Tab and that solved the problem for me.
The general proble seems to be that that particular key binding [and I believe any others in that Navigation group) were wiped out or not properly migrated on upgrade.