There are some scenario in Event Receiver when sometimes we get Save Conflict Error while uploading a single document to document library from UI, the edit properties page appears, we update the properties and save the changes, there is a possibility to get a Save conflict error. This is because ItemAdded is an Asynchronous event.
To avoid this error the ItemAdded event can be made Synchronous by doing the following:
1- Open Elements.xml file of Event Receiver and add below section inside Receiver tag....
See here my complete Element.xml file...