There are about 20 different reasons you could be getting this message. Make a backup of your data before you begin troubleshooting this problem. Save a disk image on another medium also if you can.
Google the message and see if you can find people who have solved this problem. Try their fixes first and keep records of what you do so you do not try the same fix more than once.
After failing to fix this issue on an office computer on a network, I installed a wireless dongle to bypass the nic card in the machine. After about a week the issue was resolved – I don’t know why, and I returned the machine to the network card. That was about a year ago on a Windows 7 computer and the problem has not come back.