windows 7- itunes library cannot be saved. The required file cannot be found.

My iTunes has been working fine for years. Then suddenly I cannot open it and get the above error message. My iTunes library is located on an external hard drive. I've googled and tried many different ways to fix this but all end up with more and different other error messages. One of them being the folder iTunes is on a locked disk or you do not have write permissions for this folder. I checked with the program Unlocker and nothing is locked. I tried to copy and paste the iTunes folder to a different drive but get the the error message that it can't find the file.

Thinking that something got corrupted I thought I'd just download the iTunes for computer again but the requirements say for Windows 10. This is a Windows 7 computer. So how do I fix this?