itunes 备份选项变灰，手机无法备份，怎么办？？

外国有用家有类似经验，删除plist就解决。直接引文希望楼主看得懂：

Select Finder.

Hold the option button while selecting the Go menu on the top bar.

Holding option brings up the Library in the drop down menu. Select it.(Library)

Open the preferences folder in this Library folder.

Find com.apple.iTunes.plist

(Make sure you quit iTunes)

Now move this file to the trash.

Restart your computer.

Empty out your trash.

Start iTunes again. (Don't worry, it'll automatically make a new preference file.)

Now it'll work.

http://forums.macrumors.com/showthread.php?t=1535741

我按这个步骤操作不行，去掉重启电脑这一步反而好了。。