Error 745: An essential file is missing or damaged

Reboot the computer. Do this and hope you don't have the error when you boot back up. If you do...

Reinstall Dial-Up Networking and TCP/IP or have your computer serviced. The error indicates that files needed by Dial-up Networking either do not exist or have been damaged/corrupted. Dial-up Networking needs to be reinstalled. Microsoft Knowledge Base Article Q174579 details this process. This procedure is not recommended for computer novices, and requires that you have the original installation files for your copy of Windows, either on the computer or on CD-ROM.