It is not a cookie issue at all.
The changes I made changed the line to make sure it deletes the file out of the upload directory of the user.
This is why as stated before by me you where being sent to bulkupload and triggering that error cause it was processing two files. The old file not uploaded and the new file you where trying to upload
The fix will correct the issue but for users you might want to delete all directories under uploads so they can all start fresh