The title says it partially, but that's not the whole story:

I decided to use OneDrive, and so I sent a folder from my external Toshiba drive to OneDrive. It took forever and three days to finish, and seemingly isn't finished yet.

I now get, File Failed to Upload -- There was an error while uploading a file to the server. Click to view and resolve the error.

Ha! I wish I could do something that simple, but it's not gonna happen! Nothing I do will help to resolve the error.

I've looked into the event log and everything there is all Greek to me; I've seen 1002 (101) Application Hang (among a few gazillion other things), but it doesn't tell me more than that.

I've resigned myself to losing files that haven't made it across, since I have most of them on another external drive, but it seems I can't stop whatever's happening.

Here's the first page of the viewer:

Click image for larger version