Hi,
Thank you for posting in Microsoft Q&A forum.
Per my experience, it's generally because the boot image you used for your Bootable Media is different than the one selected for your task sequence. It's wanting you to remove it so that it'll appropriately load the one copied and saved in storage.
When the boot images don't match, it downloads the correct boot image, stages it to disk, and boots off that instead.
Rebuild your bootable media with the current boot image and you may not get this message anymore.
Hope above information helps.
Best regards,
Simon
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