iTunes can't backup iPhone because a backup can't be saved on this computer

Hi. This worked for me after months of trying many different fixes. Give it a shot.

Locate the iTunesPrefs.xml on your PC. In Windows XP the iTunesPrefs.xml location is:

C:\Documents and Settings\username\Application Data\Apple Computer\iTunes
or:

C:\Documents and Settings\username\Local Settings\Application Data\Apple Computer\iTunes.

With iTunes closed, I renamed this file from iTunesPrefs.xml to iTunesPrefs.xml.backup in both locations. Then I opened iTunes, connected my iPhone, and the backup was successful.

Note that doing this will force iTunes to recreate the iTunesPrefs.xml file with all it's default settings. Any user preferences you may have set within iTunes will be removed. You will need to set any user defined preferences again.

Let me know if this works for you.

Guys I think this is might be an issue with expired me.com or mac.com accounts. I am a developer and my iPhone4 has been working and syncing just fine. My me.com (mac.com) account expired in January and was turned off. Ever since my backups fail. I've come to this conclusion only after reading all of the forums and deleting all of my backups (which now I will have to start over with over 300 apps), ensuring directory permissions were correct.

Apple needs to investigate this as an end user can not determine this when all we get is a return code of 30 and a MobileDomain error of 104.