Welcome ,I will give a full and clear answer to your question, please make sure to reply to any questions I have. They may be essential to my reply.
Hi , I will try to help , please install OSX Combo update to your system .
Please can you make sure your OSX Boot drive or Mac HD has at least 15GB space free & the size of the Project on top of this . .
If your project is 100GB that = 110GB free needed on Mac HD etc .
To avoid issues on exporting and rendering with imovie
and similar apps etc this is essential. .
Once checked , Empty trash .
A safe boot can help fix any Mac HD errors,
Turn off the Mac .
Power on the Mac .
Hold shift on the keyboard using a USB keyboard , while powering on the Mac and booting , boot to safe mode.
Once booted to safe mode , restart and boot as normal .
Full details here :-http://support.apple.com/kb/ht1455
Ok now install combo .
For Lion . http://support.apple.com/kb/DL1485
For Snow leopard . http://support.apple.com/kb/dl1399
Please can you let me know if the problem remains ,
The Mac HD should be now working , you can also make a safe boot after the combo update , and then boot as normal after .
Any change in problem ,
Also , what OSX version are your using?
What Software version for Final cut ?
What drives are you using external Or internal Media drives?
What type of Mac , imac Mac pro , etc ?
Also you stated you changed permission in the finder ? , Via get info ?
Also did you upgrade the OSX version? or Migrate user accounts from an older Mac ?