Booklet won't let me because of multiple page sizes, even if I am using A4 for all the pages, this is the error message:
"The active document uses multiple page sizes Print Booklet works only with documents that use a consistent page size."
I am using Indesign CS6 (patches are up to date)
Do you already see this when starting the Print Booklet dialog or later when finally putting out? If you can see the dialog windows, will the preview show all pages in same size?
This is a known bug. The only thing I've ever had work after that was to copy and paste in place all content to a new file.