After entering credentials using Expert Assist an error is received: "Access from IP address xx.xx.xx.xx is not permitted".

STATUS: This issue has been resolved in version 10.2, which can be downloaded from here.
WORKAROUND for earlier versions:
In host computer create a value in Registry with following information:
Hive: HKEY_LOCAL_MACHINE\SOFTWARE\DesktopAuthority\V5
Value: AllowPassthrough
Type: DWORD
Data: 544C454B (hexadecimal)
If several computers are affected a Registry element can be created in Desktop Authority following these steps:
1) Create a new Registry element with these settings:
Hive: HKEY_LOCAL_MACHINE\SOFTWARE\DesktopAuthority\V5
Value: AllowPassthrough
Type: DWORD
Data: 544C454B (hexadecimal)

2) Use Validation Logic to apply this registry element to affected computers.
3) Save and replicate.
DISCLAIMER: Support does not provide support for problems that arise from improper modification of the registry. The Windows registry contains information critical to your computer and applications. Make sure you back up the registry before modifying it. For more information on the Windows Registry Editor and how to back up and restore it, refer to Microsoft Article ID 256986 “Description of the Microsoft Windows registry” at Microsoft Support.