Having defined a test program model, the test team constructs a test architecture, which depicts the structure of the test program and defines the way that test procedures will be organized in support of the test effort.
To verify this problem, just connect your iPhone to a different USB port on the computer. Try installing/reinstalling latest version of iTunes. Install the latest version of iTunes (v12.2.1.16) for Windows 10 on your computer.
Posted By: ihelpounge Staff on: January 22, 2012 11 Comments. Itunes Error 21 is the most typical error customers face while performing a restore on the iPhone. Tool Firmware Improve mode often called DFU mode, this mode allows you to restore your iDevice with an original iOS version or a custom iOS version.osted By: ihelpounge Staff on: January 22, 2012 11 Comments. Itunes Error 21 is the most typical error customers face while performing a restore on the iPhone. Tool Firmware Improve mode often called DFU mode, this mode allows you to restore your iDevice with an original iOS version or a custom iOS version.