You may receive this message during Windows boot. It should give a filename at the bottom of the message. This particular problem is for filename vnetsup.vxd or dfs.vxd. Vnetsup.vxd and dfs.vxd is a Windows networking file. If you are receiving this message, a file for Dial Up Networking has been corrupted or is missing. Dial Up Networking must be reinstalled. You may find Dial Up Networking at this site.
Microsoft article #Q137454 provides more information on this error.
You may also recieve this message with different filenames if you try to install Dial Up Networking but it is canceled for some reason. If that is the case, Dial Up Networking must be uninstalled and installed again.
Microsoft article #Q166832 provides more information on this error.