Hi Roger, you have been a great help, I managed to solve this with your guide .. many many thanks!
For those who encounters the same, here are the steps which I followed to solve this F8 mission control issue: -
Step 1 : Finder, select Go and hit Option key. "Library" will appear. Select "Library" (while holding down Option key)
Step 2: Look for symbolichotkeys.plist. Edit this with text editor.
Step 3: Find for "75", delete it. Find for "76", delete it.
Step 4: Restart Mac
Step 5: Go to System Preferences-keyboard-keyboard shortcuts to reassign those shortcut keys which appears as a conflict.
Step 6: Go to System Preferences-keyboard-keyboard shortcuts-mission control to re-activate those shortcuts for mission control.
Step 7: Go to System Preferences-Mission Control and reassign the following:
Mission Control = F9
Application Windows = F10
Show Desktop = F11
Show Dashboard = F12
Thanks again Roger for your help.
with rgds, Gary.