[Scribus] PDF/X-3 concert rgb to cmyk?

[Adolfo José Sáez Folgado]

When I exported a file to PDF/X-3 i using a ICC color CMYK "ISO Coated
v2 300% (ECI)" but my printer said that the images are RGB
What am I doing wrong? Do I need to convert the images to CMYK previously?
Windows XP Scribus 1.3.3.11-1
Thanks
Adolph