It sounds like the original eM Client V8.x might have been open in the background and didn’t close the process 100% at that time.
Uninstall eM Client and when asked do you want to delete the database choose “No” and after uninstall, if you have Windows check that the “eM Client folder” C:\Program Files (x86)\eM Client has been deleted. If not manually delete it.
Then install the latest version of eM Client again which should pickup your exiting EMC database and open ok.
this feature you are trying to use is on a network resource that is unavailable
If you are still getting network resource that is not available, see the following threads in particular @Son-of-A-Gun post at the end of the 1st thread.