Cannot assign a drive letter to a partition from the backup archive
Ok, whats up, I've been posting regarding a backup drive that was formatted in error, I have recovered the Acronis TI 2019 backup files but Acronis says they are corrupt and won't validate!
Enter tech support feedback, I need to download the "new" TI2021 trial and create a bootable Winpe recovery usb drive, well rather than just download the trial, spent the money and upgraded my TI 2019 for 3 pc's to TI 2021 for 3 pc's! Before I was having a problem that the "validate or mount" was not available it is now available but the files STILL display as a corrupt archive and the "mount" function issues the error "Cannot assign a drive letter to a partition from the backup archive" 
Any feedback that may be helpful??
This whole problem started here! https://forum.acronis.com/forum/acronis-true-image-discussions/acronis-backup-drive-formatted-error
Have been trying to recover since, Tech support suggested the update to TI 2021, won't validate calls files corrupt!
Sorry, but given that the backup files come from a backup drive that was previously formatted then recovered, then your chances here are looking very slim at best.
Have you tried just validating the initial Full backup file on its own without the other files present in the same location (moved to another location). If you cannot validate that full backup file, then all further validation is pointless!
New!!! I have turned off "Active Protection" but I am still getting notification of vulnerabilities from April 2nd, seems TI 2021 is still very buggy! Some commands leave the program in a hang state!
On to the problem I originally posted about, trying to "add" a backup in as Acronis doesn't pick it up, and I get the errors described here with pointers to a KB that has not yet been written?? https://kb.acronis.com/errorcode/ Event code: 0x01010005+0x01010005+0x01E50015+0x01E5001A+0x0004000E
Screen Shot:
I have to confess that I have all the new ATI 2021 Protection features turned off permanently and especially the vulnerability scan tool (in the Protection Settings panel).
I did not want these features in my Backup application and prefer to use my tested & proven tools!
You do not need to Add the existing backup to the ATI GUI to be able to work with it but if it is failing all attempts at validation or opening to browse the contents of files via Explorer, then unfortunately, you are probably losing this battle!
Was there something in particular that you need to recover from the corrupt backup archive? If not, then I can only recommend starting afresh and try to follow the 3-2-1 rule, where you make 3 different backups, stored in at least 2 different locations, with 1 being stored offline where possible.
Steve Smith wrote:I have to confess that I have all the new ATI 2021 Protection features turned off permanently and especially the vulnerability scan tool (in the Protection Settings panel).
I did not want these features in my Backup application and prefer to use my tested & proven tools!
You do not need to Add the existing backup to the ATI GUI to be able to work with it but if it is failing all attempts at validation or opening to browse the contents of files via Explorer, then unfortunately, you are probably losing this battle!
Was there something in particular that you need to recover from the corrupt backup archive? If not, then I can only recommend starting afresh and try to follow the 3-2-1 rule, where you make 3 different backups, stored in at least 2 different locations, with 1 being stored offline where possible.
I agree @Steve Smith, I have my own tools for protection and don't need the added overhead and the confusion it brings to my OS!
As per your second question it has become an obsession to recover these files, the problem is twofold, first I lost my secondary backup drive due to drive failure, (waiting for new drive under warranty) and the files I am trying to recover from my current (2021) backups due to operator error trying to create a "Windows to Go" disk and not paying strict attention, inadvertently formatted over my backups (1 partition) of a 4tb external drive where my backups are normally stored!
Under TI2019 I could look at the files without mounting the drive, but that seems to be an issue now with TI2021!
Will keep trying, thanks for your feedback!
Update @Steve Smith, I have rolled back to TI2019 where I seem to be able to at least get to the info from my recovered backups, although it is a workaround involving many steps and pointing back to each volume in the "Backup set" see scrn shot! 
If there is a better way I would love to find it TI2021 bought me nothing but more confusion! Maybe a refund is in order??
TI2019 does not offer the "mount" option, which in TI2021 it is offered but doesn't work!
Since you have reverted back to 2019 and can now view the backup archive. Working with the last file in the list will get you to the latest data of all the backup files you have. Since this appears to be a full disk image have you considered recovering the image to a different disk? If you so that you can then retrieve whate4ver data it is that you need.
Enchantech wrote:Since you have reverted back to 2019 and can now view the backup archive. Working with the last file in the list will get you to the latest data of all the backup files you have. Since this appears to be a full disk image have you considered recovering the image to a different disk? If you so that you can then retrieve whate4ver data it is that you need.
Ok. I did another copy of the original Full backup file that was recovered from a formatted disk " HP2016-NORM_full_b35_s1_v1.tib" this file was copied to a new drive and is the only file from the "Incremental set" I have tried, it appears to be working and validating have not tried yet to mount the drive, but
I have also reloaded TI2019! So looks like it can be saved after all @Steve Smith
Last screenshot, file will now mount ! 
That is good news, you could try adding one of the incremental files at a time and revalidating to see if these are also able to be recovered!
Steve Smith wrote:That is good news, you could try adding one of the incremental files at a time and revalidating to see if these are also able to be recovered!
I'm making my last entry to this thread as I consider the matter closed and have returned to using TI2019 as I just found it less cumbersome to use! The files from my "formatted drive" have all been recovered from my careless mistake and would like to thank those that offered their input! Last screen shot: