Trouble Making Image Backup with Acronia True Image 2016 -- apparent misread of space

I have been trying for days now to make a backup image of my internal Windows 10 hard drive, fully updated to current Windows 10 level May 2020. I have been using Acronis True Image 2016, as I always do. I have been backing up to an external, USB2 connected hard drive with 160 GB of free space on it (a 320 GB hard drive), the same drive I normally backup to. This is a Gateway laptop, NE56R from 2012, which shipped with Windows 8.

I have been trying to backup all partitions, including the C, and recovery partitions (including the Push Button one, which is about 15 GB) and whatever others are there. In total, they are about 109 GB. So I ought to have plenty enough free space.

I have checked all partitions to back up with True Image. It runs the whole backup, takes a good five hours. At the end, it throws up amessage saying ther eis not enough space for the image.

I have never had this problem before. The machine is booted from the True Image disk, so that should rule out some issue wiht my Widows 10 OS. I am doing a full disk backup, and I am even using Maximum Compression, which is what I always use, so I should need something lessthatn 109 GB of free space. and Ihave 160 GB of free space on the external drive.

I have a backup of Win 10 I made in April, shortly before the new OS level cam out on the drive -- I always keep two, just because. I deleted the older of the two on there, so now have only the one. I certainly don't want to delete the one on there, and still have this problem but no backup at all. But Ihave more free space than shudbe needed.

The external drive has been used only for backups since I started using it brand new, and I make a backup once or twice a year -- and I have been using it no more than four years. So, the external drive has very little, hardly any actual use on it, it is not far from brand new.

I read something this morning about a real problem found in the new Win 10 update, something to do with Storage Space, that is some sort of function in the OS now. I don't know what that is, or what it does. But the story said if your drive is not showing as RAW, then it should be OK, not affected. I checked Disk Management, and none of my volumes nor the external drive are marked as RAW. So, that should mean that issue is not the case here.

I have done enough backups in the past four years using the Acronis True Image 2016 software. It has always worked fine, and actually with less free space (I had another item on the drive too, but have deleted it. I also have deleterd about 32 GB of stuff from my C drive in an attempt to make this backup fit, but to no avail -- that is, my last two backups were actually larger than this one, and they fit fine.)

So, why do I keep getting the message about not enough space? I should have way more than enough.