Elements 11 Can't use 297 x 210 format in Photo Collage

I have Photoshop Elements 11. When I use Photo Collage it offers three sizes, 210mm x 297mm, 297mm x 210mm, and 300 x 300. If I choose 210 x 297 or 300 x 300 it all works, BUT if I choose 297 x 210, the size/format I really need, Elements takes me back to Organiser in stead of arranging the images. Any idea why this is please?

I can't remember if I have used horizontal format before, I have used Photo Collage a number of times.