Header tiles don't work with the current customizations and will be displayed in compatibility view. With header tiles, you can't have more than four fields or multiline fields, and you can't use web resources and inline frames.
So if you're seeing this message that means you've probably added a either a field which is formatted to greater than a single line in height, a web resource, or an iFrame to the form header.
Normally the form would look like this:
But instead ends up looking like this:
So if you need to use one of the three offending scenarios in your header you will have to make some trade-offs. The first is the look of the fancy new tiles versus the ability to keep some important object visible at the top of the screen regardless of the vertical scroll position. The second is that any fields added to the header will now become read-only as the tile gives them the magical power of being editable.
If you aren't dead set on the top of the page for one of these items, you can always use them in the form's footer. Granted the tiles don't exist in the footer but at the same time the controls will still render as expected, which means that an actual field will still be read-only when in the footer.