Error message: This sheet is damaged and cannot be viewed.

We know of one situation where this can come up with Prism 6 Windows:

1. Enter data and make a graph.

2. Copy some data and paste it on a graph to make an embedded linked graph.

3. Go to the data table and delete all the data that is part of that table. 

4. Go to the graph. You'll see the message. And you won't be able to save your file. 

Workaround: Delete that graph entirely. 

Fixed in 6.05.