What's this error message when setting Pagination?

Using FM10 ....

I clicked Format > Page Layout > Pagination (on a file in the bookfile, not with the file open) because I want to set pagination to "Next Available" and "Delete Empty Pages".

But when I click Set, FM pops up a warning:

     The new column layout in xyz.fm seems to overlap with other objects on the Left and RIght master pages. Are you sure you want to do this?

What is it trying to tell me? Thanks.