echo465:

This is almost always caused by:
- An invalid miner launch string
- An invalid AMD/ATI SDK path
- An invalid phoenix path

to narrow it down:
1) Look in ~/.smartcoin/smartcoin.log
Any information there?  What did it show as the launch string to launch the miners?
2)  Go to the control tab->4) Edit Settings
check the Phoenix installation location and the AMD/ATI SDK installation location
3) Go to the control tab->6) Configure Miners->Edit.  Edit the path and the launch string if needed.