Taken from fmscout.
First of all you need to turn on hidden files and folders.
XP:
My Computer
'Tools'
'Folder Options'.
The go to the 'View' tab and select 'Show hidden files and folders'
Windows Vista and Windows 7:
My Computer
'Organize'
'Folder and Search Options'.
Then go to the 'View' tab and select 'Show hidden files and folders'
Then delete the following folder:
XP:
C:\Documents and Settings\<username>\Application Data\Sports Interactive\Football Manager 2012\Settings
Vista/Win7:
C:\Users\<username>\AppData\Roaming\Sports Interactive\Football Manager 2012\Settings