OK, is there is bitmap behind the vector graphic or on top of it? Are there any fonts embedded (i.e. some characters, words)?
When you open the SVG with an associated software (Inkscape, PhotoLine?), will it print flawlessly? If not, the SVG export format might not be compatible for printing.
If the file contains fonts, you might try to re-open the SVG and convert text to curves before you save and import it again.
If you can post the SVG, we could try it in different Scribus environments to check if the problem persists.
I've attached a clean SVG, which you might place in Scribus and check the PDF.