"The structure size is incorrect."

This is an unusual error...

I'd start by checking the settings for your internet connection in dialup networking, and right clicking on the connectoid, and making sure all the settings are correct. (check your ISP's manual for the correct settings)

Also make sure you are using the correct connectoid, ie clicking on the right connection.

If there is still a problem, you could uninstall and reinstall dial up networking (make sure you have your windows cd handy in case your computer asks you for it).

Or just reboot the computer, might sound crazy but that sometimes clears it up for some reason..