In our report, we programmatically create the data sources available to the user. These data sources have a connection string that just reads "UNAVAILABLE". Then, when the report is viewed, I swap out the connection strings on the server-side.
This works fine for viewing reports, and it also is fine if I'm only using tables in the designer. However, if I try to use a PictureBox in the designer, I get an error that the PictureBox can't be displayed. It still works when I preview the report, but the editor ends up in a broken state.
From my debugging, it looks like rendering the PictureBox in the designer is trying to connect to the various data sources defined for the report. I don't understand why, since it's just a URL for an image.