Error:

Unable to access target repository Error: Key not valid for use in specified state.

Resolution:

1. Disable Backup Copy Job
2. Open VBR Console and navigate to Home => Backups => Cloud
3. Select the backup chain in the right window and hold down the Ctrl key + Right Click
4. Keep the Ctrl Key pressed and select "Remove From Configuration" (If this option is greyed out, make sure the Ctrl key is being held down the entire time during these two steps.)
5. Select "Yes" to remove from Configuration
6. Select "Yes" for the "...requested by your service provider or Veeam Support"
7. Let the job complete

Then rescan my cloud repository:
1. Navigate Veeam => Backup Infrastructure => Backup Repositories => Right Click Repository Object and re-scan

Then edit the backup copy job, and remap to the job you just removed.
1. Re-map the chain you've deleted with the job (use "Map backup" button)
(https://helpcenter.veeam.com/docs/backup/vsphere/backup_job_storage_vm.html?ver=110)