This problem is prevailing faster, primarily on Command Line Interface on Windows where users are experiencing “FATAL(__LINE__): Assertion Failed <1266>: got ==sizeof<size> 1266” while JailBreaking their iPhone 4S or iPad 2. That’s why i thought of writing a post for you addressing the solution to surpass this error. Well, just navigate to General>Settings>Reset>Erase All Content and Settings and you are done.
After following the above steps, follow the JailBreak process again to JailBreak using CLI on Windows. Now, after “-i payloads/jailbreak.mobileconfig” command in the command prompt, you won’t face any “FATAL(__LINE__): Assertion Failed” error. You can checkout our guide to perform CLI on both Mac OS X and Windows. We are also hoping for the Windows version of Absinthe really soon from Chronic DevTeam.
Let’s know if you face any other error in the comment section. We would definitely do our best to find the appropriate solution of your problems. In majority of the cases, the re-jailbreak would fix many of the issues. This solution is tested and works for us.