Install the program again then check if this fixes the problem.
Use a disk utility application to check the system. After booting, check your machine for any possible errors. Uninstall the application then restart your computer when asked. You may also try reinstalling the application to free your system from any corrupted files that are probably affecting the whole process. If you are trying to use the program during peak hours then maybe you should try it after a couple of hours or during off-peak hours to have a better connection. You should also check if your network is not experiencing heavy web traffic that reduces the connection’s speed.
Since the program requires an internet connection, you should check the network cable at the back of the CPU if it is connected and attached properly to the port. Read the StarWind blog article to see the difference between ESXi 6.5 and 6.7 and decide whether it is necessary to upgrade your system to VMware vSphere 6. The next thing to check is your computer’s network connection. See if there is a change after rebooting. If this is new installation, try closing the application, restart your computer then try it again. The problem here is either a connection-related issue or a problem with the program itself.