At present, it's nearly impossible for multiple people to work in Proclaim at once. But, there's now way to know if there is someone else logged in at another location. I was having all kinds of problem adding in our music for tomorrow's service. So, I called around. Turns out the senior pastor was putting his sermon slides in. He, too, was having difficulties. Once I quit the application, he was able to continue to work with no problems.
We either need to fix this major bug or provide us some kind of alert that lets us know other users are logged in working on the presentation.