Uninstall the driver then try again, correctly
This has instructions, but I can't copy/paste them to here.
Cmd/F to search, then search in the 'extra' box inside the page, not Safari's usual search box - for 'uninstall'
It will take you straight to the Mac uninstall page.
I got it… but I really hope you're not doing this on Yosemite… unless you have unsigned kexts switched off
MAC OSX Driver Uninstallation
Note: The device must be safely removed from the computer before beginning the uninstallation.
To begin the uninstallation process, open up a command terminal and enter the removal command
sudo rm -rf /System/Library/Extensions/LAN9500.kext/
This causes the device driver to be removed from the operating system.
The final step is to remove the network entry that was created during the installation process. Click the systray network icon (top right corner of the screen) and select “Open Network Preferences...”