I just installed a software update that I was prompted for, presumable affecting Xcode. Now when I start Xcode, I am presented with a dialog box which states that Xcode must install the Mobile Device Framework before continuing. When I try to do this, after providing my password, it fails with "An unknown error occurred. See the install log for more details." I do not see anything useful in install.log that identifies the problem. I've tried re-installing multiple times and rebooting to no avail.
I'm currently running Xcode 4.3. Perhaps I need to upgrade to 4.4? Has anyone else run into this problem?
This problem has once again appeared in Xcode 11.1 and is caused by an invalid certificate that expired some day in October 2019.
You can work around the problem by temporarily changing the system date to before the certificate expiration date.
In the case of Xcode 11, set the system date to Oct 3, 2019, run Xcode, then change the date back after the components have installed.