1. You create a backup using Version 12 backup format (this format is used by default for all new archives in Acronis Backup 12.5 and Acronis Backup Cloud).
2. Task fails with: "Input/output error"
This is a generic error that requires investigation.
For Acronis Backup 12.5: Please update the product to the latest available build (13400) as Acronis Backup 12.5 Update 4 contains fixes of this error message. If you need assistance, collect system information from the affected machine and contact Acronis Customer Central with a reference to this article