The specific error is:
Script: \\dc\netlogon\folder\file.vbs
Line: 0
Char: 1
Error: File not found
Code: 800A0035
Source: Microsoft VBScript runtime error
The file is at the location specified. Furthermore, the same error is generated when double clicking on the file directly. And if the file is copied to the local drive and double clicked. And if invoked from the command line with wscript. It appears to occur when ANY vbs is launched via ANY method.
WScript is not disabled through the registry.
It turns out I was including other scripts using code like:
This is the file that could not be found, but the parser choked - maybe because of the combination with the executeGlobal command - and gave me line 0 instead of the actual line.
So it turns out that line 0 probably references a combination of parsing error and inner reference file not found.