The Toad icon is not accessible on a client machine from the citrix server connection. Whenever a user tries to connect on client machine from the citrix server, it does not respond.
The file looking is at a different location.
Go to the location where Toad is installed (Toad directory), copy the Toad.ico and paste the file in the relevant directory on the citrix server. For Example: C:\Program Files\Quest Software\Toad for Oracle 9.6\toad.ico