git reset causes web.config not to be readable

I've managed to get my codebase/repository/machine into a state where git reset --hard breaks my code and closing/re-opening the sln in VS fixes it.

Specifically:

• Open the Code base
  • Rebuild & Run
  • Site runs fine
• run git reset --hard
  • Rebuild & Run
  • Site fails with <Error_below>
• Close and then re-open VS
  • Rebuild & Run
  • Site runs fine
• run git reset --hard
  • Rebuild & Run
  • Site fails with
• Rinse, Repeat, ad nauseum.

Error Details:

• HTTP Error 500.19 - Internal Server Error
• Error Code: 0x80070003
• Error Message: Cannot read configuration file
• Config File \?\C:\Work\Project Source code Folder\Website\web.config

Obviously I've checked that the config file is present, in the correct place, and is well-formed (no unclosed tags, etc.) at all points.

My First guess was file permissions but neither chmod web.config 777, nor Window permissions > Everyone -> Full Access made any difference that I could tell (possible that I miss-applied them, though?)