Use the CasTool.exe /d command to debug the tool. The feature proves especially helpful when registering or unregistering from a parent server results in program errors or unsuccessful attempts.
To debug CasTool.exe:
Start CasTool.exe.
Execute the debug command in conjunction with the register or unregister command. For example:
Register a child server:
castool /d /n:{parent server user account} /p:{parent server name:port} /c:"{child server display name}"
Unregister a child server:
castool /d /u