"The string could not be converted."

This is an odd error...

I'd suggest start by rebooting the machine, and/or making sure all other applications are closed..

After you have checked your ISP's connection settings in the Dial up Networking Connectoid and the tcp/ip stack in Networking in the Control Panel, you could uninstall/reinstall Dial up Networking and/or the TCP/IP stack in Networking in the control panel (Note, make sure you have your windows cd handy before you do this since your computer might ask you for it during the reinstall).