The instructions (which came from a post on sageforum.co.uk of which I am a moderator) below will allow you to do a full uninstall and reinstall. You should only do this if you don't have Sage Payroll installed as well.
Before you start make sure you take a copy of the ACCDATA and MEMO folders and, if you have any amended layouts, you may also want to copy the REPORTS and LAYOUTS folders too.
First of all use add/remove programs to remove any installed versions
The delete these folders;
Sage program folder
C:\program files\sage
common files
C:\program files\common files\anything to do with sage
data directory (Windows XP)
c:\documents and settings\all users\aplication data\sage
Then delete all shortcut icons from desktop, start menu, anything else obvious you can see
Then open C:\windows\system32
In here view file details, add the column for 'Company' and sort alphabetically, delete all files where company is;
Sage
Sage UK
Sage PLC
Sage 50
(You get the idea - use common sense)
That should remove almost everything, anything else in registry, ODBC drivers etc would be OK to leave, they wouldnt stop program from opening
When re-installing program, use CD, run a custom installation to a brand new location, such as;
C:\sagev2011
Make sure installer finished with no issues.
Open program using the new shortcut icon you should have on desktop
If you have further issues, you may have to un-install & re-install MS .NET framework 2.0
Or, download a Sage SBD Desktop Installer Utility, but try all above first.
Other forum users have reported that this did solve the problem but, as it involves manually deleting files/directories, you follow it entirely at your own risk.