The last back up failed

Are you using more than one destination drive for your backups?  If you are, then this can cause this type of issue because each drive presents a unique identifier which is recorded in the internal Acronis Database used to track task activity.

The other thought is whether your external drive is getting the same drive letter each time that it is attached?  If the drive letter does change, i.e. because you plug in a USB stick etc, then try using Windows Disk Management to allocate a drive letter which is further down the alphabet that would not normally be allocated, so that the drive always is given that same drive letter when connected.

If you don't already use it, download a copy of the MVP Log Viewer tool from the Community Tools link in my signature and use this to check for any error messages being recorded in the log for your backup tasks.

Thanks Steve for your reply.

The destination is the same hardrive but different sub folders. Which I always used without any isues, also the drive letter is always the same 'F'.

Here is the log of one of the backups 

3/28/2018 9:22:44 PM: -05:00 12368 I00640000: Backup reserve copy attributes: format tib; need_reserve_backup_copy false;
3/28/2018 9:22:44 PM: -05:00 12368 I00640002: Operation Data 2+4 started by schedule.
3/28/2018 9:22:46 PM: -05:00 12368 I00640000: Backup reserve copy attributes: format tib; need_reserve_backup_copy false;
3/28/2018 9:22:46 PM: -05:00 12368 I013C0000: Operation: Backup
3/28/2018 9:22:46 PM: -05:00 12368 I0064000B: Priority changed to Low.
3/28/2018 9:22:46 PM: -05:00 12368 E000B0428: Error 0xb0428: The backup location was not found on the destination drive. Make sure the correct storage device is connected to the computer.
| trace level: error
| line: 0x4d3f22948e29f39c
| file: c:\bs_hudson\workspace\245\products\imager\archive\impl\utils.cpp:709
| function: TrueImage::Archive::CheckVolumeDeviceIdMatch
| line: 0x4d3f22948e29f39c, c:\bs_hudson\workspace\245\products\imager\archive\impl\utils.cpp:709, TrueImage::Archive::CheckVolumeDeviceIdMatch
| Path: F:
| $module: ti_demon_vs_10640
3/28/2018 9:22:46 PM: -05:00 12368 E013C0005: Error 0x13c0005: Operation has completed with errors.
| trace level: error
| line: 0x9f2c53c72e8bce56
| file: c:\bs_hudson\workspace\245\products\imager\demon\main.cpp:608
| function: main
| line: 0x9f2c53c72e8bce56, c:\bs_hudson\workspace\245\products\imager\demon\main.cpp:608, main
| $module: ti_demon_vs_10640

Start: 3/28/2018 9:22:44 PM
Stop: 3/28/2018 9:22:46 PM
Total Time: 00:00:02

Your error log shows that no destination is selected for the backup .tib file of drive F:  It simply shows | Path: F:

I would suggest that you select the backup task in the application GUI then select the destination again just as you did when you configure the task when you created it.  When you have the final path folder selected click on the Ok button so that the app will save your choices.

This should update the app and I think will fix your problem.

Thank you all for your help.

It seams to be working now. I created new backups, before I was cloneing the backups, I assume that if the original backup wsn't working when coloning it the issue was also coloned.

Sounds right.

I sort of have the reverse "problem". True image failed (in one instance) when the drive letter changed, and succeeded (in another instance) when the drive letter changed.

I use an external USB hard drive for my backups. On the first backup, It was D:. In a later, incremental backup, it was E: and the backup wouldn't run (red X). Support told me to keep the drive letter the same.

So far, same problem, same solution.

But then I was testing a "Rescue" flash drive, and it wouldn't boot if the external hard drive was attached. So I unplugged the external hard drive, did the boot from the flash drive, and then plugged in the hard drive. That worked. So far, so good.

Afterward, I booted normally, but I forgot to remove the flash (rescue) drive. Windows came up normally (because I hadn't told the system to include USB in the boot). But I hadn't noticed that the external hard drive was now E:.

Later, Acronis tried to do another incremental backup. To my surprise, it worked.

So, it looks like True Image found the USB hard drive, even though it was not at its normal (D:) drive letter.

I am confused. Why did it fail, one time, with the wrong drive letter - and succeed, another time, with the wrong letter??

Welcome to these User Forums.

I would recommend checking your backup drives to confirm that your backup image has actually been written to the correct / intended target drive?  There have been instances where having another drive using the normal target drive letter has been used, including creating any target folders on that 'new' drive.

I have seen the same issue with having an external USB drive connected when trying to boot from my USB rescue media, where the computer has tried to boot from the drive and not found a valid OS and stopped to complain instead of checking the next USB device.

Drive letters may change simply by having a USB drive connected from boot time, versus the letter that is assigned when connecting after booting.