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Error 745 - An Essential File Is Missing (win95/98)

This error occurs with Dial-Up Networking (DUN). An explanation & fix is offerred below.
Causation
This error message is caused by either:
  • File corruption/removal, and/or
  • Removing Compuserve software (win95)

    The error is due to either a wrong, missing or corrupted file handling the Session Management Module (SMM) aspects of DUN.

    Compuserve enters the picture because its WOW! service (software supplied with Windows 95, the service discontinued January 1998) replaced a Windows®' system file with one of its own files, both on disc & within the Registry. Removing Compuserve removes the file but does not change the Registry file-reference. Unfortunately, reinstalling DUN does not fix the problem, & it is necessary to hack the Registry.

More information is available in Q174579 on the Microsoft knowledge base.

One sequence of events that can cause this is removing the Compuserve software provided with Windows 95.

Discovery Work Beforehand
The SMM aspects of DUN is handled by one of two Windows® files: It is therefore necessary to first discover whether Dial-Up Scripting is installed. This can be done by looking at the Windows Setup tab of Add/Remove Programs in Control Panel. Open the Communications section, & if Dial-Up Scripting has a tick next to it, it is installed in the system.

The final preparation step is to check for the relevant file on disc. The simplest way to do this is to use Windows® Find to search for the relevant file. The files should be in the Windows\System folder - check both size & location. If the relevant file is either missing, the wrong size or in the wrong location it will need extracting from the Cabinet files.

Fixing the problem
Open the Registry: Look now in the right-hand pane to see the value of either: There is one of two legal values for this key: Any other value means that the Compuserve (or other) software has changed this key, & it will need changing back: If the value is correct, then the file on disc is either missing or corrupted, & will need replacing from the Windows' Cabinet files. Rename any existing files to have an ".old" filetype & extract new files from the Windows cabinet files.