Hello,
First I do not do Professional Desktop publishing, only small projects for my club. Here is the problem I encountered.
I opened Publisher with a single page. Then made a Master page with a gray background and a graphic banner at the top (a png image). Save it ok, reloaded it ok. THEN, I applied the Master page to my one page document. Saved it. Tried reloading it. Received the Unhandled exception error. Tried numerous times with several new documents, same result. Any time I applied the Master page and saved, the next time the project loaded I got the same error and project would not load.
Out of curiosity, I uninstalled the latest BETA ( .58) and reinstalled the previous one, ran the program, created the same project, saved it, closed it. Opened the project with no errors reported, worked as expected.
To summarize: A project with applied Master Page for me works properly and loads properly after saving when using the BETA 1.7.0.57 and does not work properly with 1.7.0.58. I am using a Dell XPS 8930 with 12GB ram running Windows 10 64 bit.