Find the file icon, which likely still exists in your project as Media Missing, and delete it.
You cleared it off the timeline, but it's still in a bin somewhere.
I have got one project like that.
File is long gone from the project and Premiere keeps on asking for it.
I also think this is caused by a crash.
Nope. It's NOT in the bin.
This happens a lot, actually, with other projects. I clear something from the timeline and don't need it. So I clear it from the bin and delete the source file. But every time I open the project, it wants it.
Have you tried creating a new project and then importing the vexsome one into it?
Might help. Can't hurt.
No, I have not tried that with this project. I've just been dealing with it. Wish I knew a way to fix this but such is life.
Thanks for the help, everybody. It is what it is.