Hi Andy,
From the issue you mentioned, either your device does not have internet connection or the host server url is wrong.
first verify the device has internet access.
Bring up the explore on device and type the tomcat server URL, like
http://192.168.1.123:8082, you should be able to see the welcome page of tomcat Apache on your device.
If you did not see the welcome page, please verify whether you have activeSync running and what is the status. And also check the connection setting is set to internet through File -> connection settings -> The Internet (For this computer is connected to drop down list)
Second, verify the host server URL is correct:
Typing the host server url into device's browser, you should be able to download and install the client directly.
Regards,