FortiClient 4.0.2284 problem with installing newer FortiClient

present FortiClient 4.0.2284 uninstalled using Control panel - Programs - Program and Features -> Uninstall - no problem, no error; OS restart FortiClient 6.0 installation fails - message: previous version detected (same when try to install ver. 5.6 or 6.4) ver. 4.0.2284 can be reinstalled again and works properly then, after uninstallation same problem occurs - newer version can't be installed No fcremove.exe tool for ver. 4.0.2284 found to download. OS W10 Pro; Same version 4.0.2284 was upgraded to ver. 6.0 on 10+ devices with no problem Any suggestion prior to reinstalling device?