I have been looking for a solution for this. I encountered this problem when combining the recordings from 2 different devices in the same project. The resolution/frame rate etc weren’t the same. This is in sony vegas 14*. Only the video I ha just recorded and added turned up green and the video I had edited before in sony vegas was intact.
To fix the issue I tried everything suggested in here but this seems a bit excessive to do. What worked for me and, is fast to do, is to download a video format converter (I am currently using the Handbrake software) and slightly change the properties of the video. I personally had to edit resolution and frame rate to match the values of the video I had already edited in sony vegas.
Hopefully this helps some folks like myself who couldnt find a solution for this anywhere and who have tried the renaming of the plugin which did not work.