After saving the logo or screenshots in a template or workspace there is an issue in the ULS log: The File with the URL "...." does not exist in this webpage.
Try to open the CM Picture Library with "URLofYourRootWeb/CMPictures"
If you get an 404 Error please navigate to your Central Administration.
Navigate to the "Web Application Settings" in the Collaboration Manager sub menu and deactivte the Collaboration Manager on the specific WebApplication(s).
After that activate it again.
Now there should be a CM Picutre Libray - please try "URLofYourRootWeb/CMPictures"