This was posted in the Symphony Forum here and I can safely say after clearing 2 pcs with this error, this was the only way to fix it. I had used beta 2 until recently and had issues and was just going to go back and use Lotus Smartsuite which still runs and works(I have that client that uses Approach) when the announcement came out to use beta3. Now I have to reload all my plugins too.
Symphony 1.3 installation issue
Please uninstall Symphony 1.3 from Control Panel -> Add/Remove Programs first and then install again.
If you don't see Symphony listed in the Control Panel(OR in my case it would not uninstall), you can use manual uninstall process below.
1 - Close IBM Lotus Symphony if it is running.
2 - Use the Windows Installer Cleanup Utility to remove IBM Lotus Symphony. You can download the utility from the following location: http://support.microsoft.com/kb/290301.
3 - Delete the desktop icon and Start menu item.
4 - If it is running, end the soffice.exe and soffice.bin processes from the Task Manager window, then remove the installation folder, for example, C:\Program Files\IBM\Lotus\Symphony.
The utility in step 2, Windows Installer Cleanup Utility, will appear in your programs list without a folder.