I am having an intermitent problem with Lightroom 4.1 Release Candidate. Sometimes when I am viewing photos in the Library module and I switch to the Develop module, suddenly, there are no images in the filmstrip. If I happen to have had a picture selected in library, when I go to Develop, it's gone. I get the message "No Photo Selected". There are no photos in the filmstrip either.
There is nothing left to do but quit LR and restart. It often takes multiple restarts to get it to work properly.