Hi
I had the error 29 for days and tried all sort of things, in the end I decided to try changing the battery as described by many forums, I bought a proper Apple battery APN 616 0435 and one of these from ebay
http://www.ebay.co.uk/itm/IPHONE-3GS-MOBILE-PHONE-GOLD-BUSINESS-1930mAh-BATTERY-/320710508791?pt=LH_DefaultDomain_3&hash=item4aabd600f7. ichanged it to the apple one first and still got error 29!! GRRR so i thought what the heck I might as well try the gold business battery....guess what! it worked and is working perfectly now!
hope this helps Wombatt