Here are Apple Steps: http://support.apple.com/kb/TS3694#error23
Error 23 seems to be associated with water damage in many cases. Some believe it is due to damaged baseband chip which is on the Logic Board. The Error Group 23,28,29 seems to be associated with the charging circuitry. Some report success of fixing Error 23 with battery or dock replacement.
If you have Warranty or AppleCare Coverage take iPhone to Apple for resolution. If no Warranty, follow Apple Steps I referenced for you above. If still problems you could try battery replacement or dock replacement.