Encore project corrupt relatively easily and once there is a problem, it is difficult to sort out.
The only easy problem is when you move things around (I.e. different drive) and have not saved it again.
The Encore project file is at the top of the folder structure for that Encore project. And if you moved any of the folders inside that structure, it won't work. Move the folders back so that you have folder-that-holds-the Encore-project file/all-other-folders-for-the-Encore-project
If you've moved assets (which are not in that folder structure), you can relink them, but that requires getting the project to open.
You might also create a new project and do the basic recreation (import menus frm the old project; import assets etc) and see if it fails at some point that might indicate a faulty file.
I would save a copy (which you probably already have), and try deleting the transcode/session files.
I fear it may be the fact that the file has moved, I remember previously I renamed a folder and the project only opened when I changed the name back.
This is probably more of a windows question, but is there anyway to find out the original file location / folder structure of when the project was first created or last saved?
is there anyway to find out the original file location / folder structure of when the project was first created or last saved?
I don't think you have to worry about that. The "outer folder" for Encore is just like a root. Whereever the Encore project file is, it doesn't care about any folders except the ones below it. (Except for permissions which is a whole 'nother problem; and might create your issues. But let's assume permissions are not the issue.) You just have to be sure that you didn't change the names or relations of the folders under the project file.
The most common error here is renmaing the project file or putting the project file inside one of the folders that needs to be below it (so it doesn't "see" what it is looking for) or moving it without moving the folders with it.