Based on the error this can be one of 2 things:
1) A permissions issue with the account you are logged in and trying to uninstall with.
2) There could be an issue with the path name.
1) Check that you are uninstalling with the install user or the server admin account.
2) You can delete the Spectrum directory. In order to clean up the registry, you should first back up the registry, and then remove HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Aprisma Management Technologies.