User profile for user: taco75
taco75 Author
User level: Level 1
4 points

iOS 26 upgrade failure (error 100), iOS 26 backup restore failure (backup was corrupt) from iOS18

I have an iphone 15 plus (iOS 18.6.2) that failed to upgrade to iOS 26.3.1. The error looks like:

"iPhone update error 100 06a6 0064"

I guess Error 100 indicates insufficient storage. The phone became a brick and stuck in DFU mode. (A)


Now I got an iphone 17 pro (iOS 26.3.1), brand new. It failed to restore from my offline backup (with iOS 18.6.2) due to the following error:

"iTunes could not restore the iPhone because the backup was corrupt"

I guess iphone cannot restore iOS 18 data on iOS 26. (B)


Then as we all know, you cannot downgrade from iOS 26 to iOS 18 on any iPhone. (C)


Combining (A),(B),(C), it seems losing data when upgrading to iOS 26 is inevitable, once condition (A) is triggered. I am stuck with 2 phones (one incomplete iOS26, one complete iOS26), backups in iOS 18, and no data can be recovered at this point.


I don't have iCloud backup due to nature of work-related data, but I have offline backup on iTunes before the first phone bricked. I don't have opportunities to upgrade OS for any versions in the middle due to nature of work. So please refrain from saying it's my fault not paying for iCloud etc. Are there any suggestions how to move forward and recover some data from backups?


Some ideas, not sure how to execute:

1) Will apple customer service provide a temporary iOS18 phone to customer, so I can store my backup on it, then upgrade it to iOS26? At this point iOS18 is like non-renewable resources.

2) Will apple software department be able to provide a rescue iOS 26 image (.ipsw), so people can "upgrade" while it only contains essential functionalities to make upgrade pass, and takes minimal disk space? This would fix the Error 100 issue.

3) Will iTunes enable restoring iOS18 backups on iOS26, instead of erroring out saying "corrupted"?


These all look like software quality issues in iTunes, iOS that are reproducible, may impact many users. Are there ways to raise awareness at all to the company? Thanks for reading.

iPhone 17 Pro, iOS 26

Posted on Mar 7, 2026 9:50 PM

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6 replies
User profile for user: SravanKrA
SravanKrA
User level: Level 10
438,344 points

Mar 7, 2026 10:47 PM in response to taco75

taco75 wrote:


"iPhone update error 100 06a6 0064"

This has nothing to do with the iOS version.


The error “100 06a6 0064” is an iPhone update failure code that typically appears when updating via a Mac or PC. It indicates that the update process was interrupted—most often due to insufficient storage, a corrupted .ipsw file, or a faulty connection issue between the device and computer.


  1. A corrupted ".ipsw" file
    1. Always use IPSW files from Apple’s servers or trusted sources to avoid corrupted or malicious firmware.
    2. Apple only allows installation of IPSW files that are currently “signed.” If the file is unsigned (older versions), iTunes/Finder will reject it.
  2. Faulty connection issue between the device and the computer.
    1. Search for accessories that have completed MFi certification. Once an accessory has completed MFi certification requirements and is reported to Apple as sold/distributed, it will be searchable in our public database of authorized Lightning, headset, charging, iAP-enabled, and Find My network-enabled accessories.
    2. Learn how to identify counterfeit or uncertified Lightning-based accessories.
  3. Ensure you have enough storage on both iPhoen and Mac/PC:--> Manage storage on iPhone or Free up storage space on Mac






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User profile for user: SravanKrA
SravanKrA
User level: Level 10
438,344 points

Mar 7, 2026 10:33 PM in response to taco75

To improve my understanding of the phenomenon, it would be highly beneficial if you could share a full screenshot (Do not crop it). Visual representations carry a greater impact than written descriptions.


Please remember that this is a public forum, so when attaching a screenshot, please avoid including any personal credentials such as IP addresses, card details, email IDs, Apple IDs, IMEI numbers, serial numbers, phone numbers, order IDs, or any identifiable location information if you are sharing a map.



With the limited information that you have provided, It is hard to even guess the problems faced by you. 


You may get faster and better responses to your query by --> Writing an effective Apple Support Commun… - Apple ...



Please re-post with detail so that someone else can help.



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User profile for user: taco75
taco75 Author
User level: Level 1
4 points

Mar 7, 2026 11:00 PM in response to SravanKrA

The error “100 06a6 0064”, essentially is about insufficient storage, because all other factors resulting in this error have a solution: use correct upgrade file, use correct connectors, etc.


Insufficient storage does not have a solution. I don't know if there is a way to remove some system/user files so that upgrade can pass. Apple does not design a workaround to this issue, which seems to be quite common. PC upgrade via iTunes does not calculate the right reserved space to prevent this either, meaning it's a software bug. I was told by 3rd party iphone technicians that, iTunes does error out and stop user from upgrading when the available space is lower than a threshold, but that threshold is smaller than what iOS26 upgrade would actually take.

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iOS 26 upgrade failure (error 100), iOS 26 backup restore failure (backup was corrupt) from iOS18

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