Installation / Deinstallation stop with an error

Please goto:

On x64 System click at 'Download X64 troubleshooter', on x32 System click at 'Download X86 troubleshooter'.
(In case your windows explore shows C:\Program Files  AND C:\Program Files (x86), then you have a x64 System)
Run the troubleshooter, remove PureSync with it. Then you can install e.g. the current version of PureSync.