Reference cannot be uploaded because it has an invalid RefID

This error occurs when references are uploaded in a source file (RIS, CSV etc.). When the file does not have a valid RefID or ID Tag, there is no way for DistillerSR to "order" or identify the references. The best solution is to either create the ID Tag in the source file and re-upload it, OR use the Sequential RefID starting at option under the Standard Options, Assign RefID section on the Find and Import References screen in DistillerSR while importing your references.