Is this a windows server?
I would suggest you check your uploads directory permissions and ensure they are READ WRITE EXECUTE. You might want to get with your host on this.
We clearly delete all files in the uploads directory of the user after processing via an unlink command
Code:
Content visible to verified customers only.
It would appear if your saying your uploads directory still has these files your host has some permissions architecture that is not allowing the deletion of the uploaded file.