iPad won't update from iTunes on my PC

Error 1100 relates to iTunes. Ensure that iTunes has been updated to the most recent version.

This external article may provide some useful guidance:

https://www.clarifyhow.com/itunes-error-1100/

Otherwise, your best option would be to seek assistance at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP):

Genius Bar Reservation and Apple Support Options - Apple

maybe error 1100 - Apple Community

Rudegar will have seen you reply in exactly the same way that I have similarly seen your reply.

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