What computer operating system is your Premiere Elements 12 running on? Have you updated 12 to 12.1 Update using an opened project's Help Menu/Update. If not, please do so.
This is my take on your question.....
For your immediate questions about Premiere Elements 12 and Adobe Revel. My first impression of Premiere Elements 12 Adobe Revel were not all that favorable. My thoughts and details on that can be found in my blog post on the subject.
Where is all this saving to Adobe Revel taking place - in the Elements Organizer 12 or as an upload of a Premiere Elements 12 Timeline content using Premiere Elements 12's Publish+Share/Private Web Album?
a. Elements Organizer 12 - Create/Slideshow/Slideshow Editor
If you wanted to keep this an all Elements Organizer activity, you cannot create a slideshow in the Elements Organizer Slideshow Editor and then use
the Elements Organizer/Share/Private Web Album to upload it to Adobe Revel. Adobe Revel only accepts photos for this feature there. And, the slideshow created for output is in a video format. What you could do, is select individual photos in the Elements Organizer and use the Adobe Revel Share/Private Web Album and arrange for the creation of an album at the Revel account.
b. Elements Organizer 12 - Premiere Elements 12 Integration
Create your slideshow in the Elements Organizer 12 Slideshow Editor, output it to Premiere Elements 12 with the Elements Organizer output option "Edit with Premiere Elements Editor", and then upload the Timeline slideshow to Adobe Revel using Publish+Share/Private Web Album. That should give you a AVCHD.mp4 slideshow at Adobe Revel.
c. Other - All in Premiere Elements 12 - create slideshow and upload to Adobe Revel using Publish+Share/Private Web Album.
Please review and consider, and then we can discuss it further. Any questions or need clarification, please do not hesitate to ask.