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, type the following into your browser address bar:
In UK and Europe, type in: go.accessacloud.com
In Asia Pacific, type in: go.access-workspace.com.au
This takes you to your own Evo apps screen.
Log out of Evo can close the browser tab.
Open another browser tab and type the following once more to go to the main login screen:
In UK and Europe, type in: go.accessacloud.com
In Asia Pacific, type in: go.access-workspace.com.au
You should now be able to select the impersonation option successfully.