Hi Christian
As the installation cache has been removed it is not possible to uninstall PicoScope. However, it is possible to remove the installation from the MSI database to allow you to install a later version of PicoScope. The later version should overwrite the old application, drivers, etc so there is no need to go deleting anything else on the system.
In order to remove PicoScope from the MSI data you will need to use MsiZap. We are not authorised to redistribute this utility but the following link will give you some instructions and download links.
http://msdn.microsoft.com/en-us/library/aa370523%28VS.85%29.aspxThe product code is as you previously posted, B99FD0AD-77EB-4511-B5DE-EC5F7BC3CBFD. This will be different for other versions of PicoScope. You will need to use the following command:
msizap /tw {B99FD0AD-77EB-4511-B5DE-EC5F7BC3CBFD}