Below are some resolutions for your 598U by Sierra Wireless device:
The internet browser is incorrectly configured.
Check the connection settings of your browser to ensure that no conflicting settings exist.
For Internet Explorer, click Tools > Internet Options and select the Connections tab. Ensure that the option Never dial a connection is selected, or that the Sprint Connection is set as the default. Also ensure that no proxy information is specified by clicking on the Settings button and ensuring that the checkbox labeled Use a proxy server for this connection is unselected.
For Mozilla Firefox, click Tools > Options and select the General tab. Click the Connection Settings button and ensure that Direct connection to the Internet is selected.
For other browsers, consult the software manufacturer for assistance.
If these steps do not resolve the issue, then please contact us for assistance.