iPod Touch will charge but won't play when connected to a Sony docking system
I found a product description on the Best Buy website: 


  The ICF-CS15IP is Compatible with most iPod® and iPhone® models, including iPhone 4. Works with: iPod touch® 2nd, 3rd, &amp; 4th generations, iPod nano® 3rd (video), 4th (video), 5th (video camera), &amp; 6th generations, iPod classic®, iPhone® 4, iPhone 3GS, and iPhone 3G.


Your 4th generation iPod Touch is listed as supported by this device, so you should contact Sony and expect them to help you.