I’ve been using licensed installation of Aspose Slides for Reporting Services on a quarterly basis since 2010. In the most recent instance, the “Evaluation Only” watermark has reappeared on exported ppt or pptx files. This happens even with reports that previously (last quarter) exported fine.
I have observed the information shared by you. Can you please share that by using which version of Aspose.Slides, you are encountering issue. If you are using Aspose.Slides for Reporting Services 4.8.0 which was released on 13 May 2013 then you need to check the license valid subscription date in your license file that it has expiry date after the mentioned product release date. You may need to renew your subscription in case your subscription is expired and you ought to use the new version on your end. If the license hold valid then please share the license file with us by following guidelines mentioned here.