
Hey Berkay,
It's a compatibility issue from what I understand. CDJ-400 are the lowest form of Pioneer CDJs that is recognized by the Traktor program. Use this PDF file, follow the instructions, and you'll be able to make your CDJ-350 compatible with Traktor. I myself run with Traktor Pro 2.0 and I followed the PDF file and am now using software and hardware smoothly.
http://pioneer.jp/support/download/dj-e/pdf/CDJ-350-TRAKTOR-PRO_En.pdf