This issue occurs if you are in your own Evo 'My Account' section and use the switch account within here. To resolve this:
Launch Access Evo then in the top right select switch account.
If you are unable to find the Switch User option, then type go.accessacloud.com into the browser address bar.
This should take you to your own Evo apps screen.
Log out of Evo can close the browser tab.
Open another browser tab and type go.accessacloud.com once more to go to the main login screen.
From here you should be able to select the impersonation option successfully.