Try this: http://www.ehow.co.uk/how_6628716_fix-iphone-unknown-error-1618.html. It can also mean a corrupt iTunes installation. Assumiing you have windows, try uninstalling iTunes and all of its components as by following this guide exactly: Windows XP or Windows Vista/7, then reinstalling iTunes. You must follow this guide exactly or it will not be successful. Note: uninstalling iTunes will only remove the application; it will not touch your iTunes library or data.
Hi Good Day! Just Try to Repair your ITUNES Go to Control Panel > Uninstall Program> Itunes > then Click repair After that Restart your PC
Proven By me. Coz the same problem with me, when i'm trying to restore my 3gs to iOS 4.1 the White Screen comes and after that the apple logo then the loading loop and iPhone shut Off, and Error 1618!!!!!!
SOrry for my Grammar