Can't add files to disk image .sparsebundle

Hi Folks,

I created a number of encrypted disk images as sparsebundle on an external hard drive. They are formatted Mac OS Extended with Apple Partition Map. When I created the images I used a 2011 iMac running 10.6.8. I have been able, in the past, to use the external drive with other machines running different systems with no issues.

I thought after all this time, it might be a good idea to upgrade the OS on the iMac, and my machine can only go up to 10.13. So I got a couple new Crucial 1TB SSD and did a clean install of 10.11, ran all updaters, and then migrated my data from the iMac. Then I took another drive, formatted it for APFS and installed 10.13.6, ran updates, and then migrated the data from the new 10.11 system I created. That was the only way I was able to upgrade it from that many systems ago. I currently have it installed in a MacBook Pro 13 from 2012. I wanted to make sure the system was in good working order before installing it into the iMac. It is still in the MBP now. So far there have been no issues.

I created some files that I wanted to transfer to one of the encrypted disk images, so I plugged the drive in, opened the disk image, and when I went to copy the files into a folder I got the circle with a line through it, and the files bounced back to the original folder. I thought that was curious. I kept trying different ways to copy into the disk image - folders, one file at a time... but no luck.

So, the Get Info window is where this all gets a little goofy. I have the check box on "Ignore Ownership on this Volume" selected. I also tried checking and unchecking the "Shared Folder" checkbox. When I unlocked the padlock on the bottom right, I'm not able to make any changes to anything. It's all greyed out - the gear icon, the +- buttons and and the names in the window. The window with my name says Read & Write, but above the box it says "You can only read." Under my name has "everyone" listed with No Access.

Is this an issue with APFS and Apple Partition map volumes? Something else? I'm at a loss. I can usually figure this kind of stuff out, but now I need the collective genius of the community. I tried to be as detailed as I could, so responders didn't have to ask a lot of questions and you have all the info you need. Sorry if it was a bit long-winded, but I thought that it may have something to do with the cumbersome upgrade process I had to do from Snow Leopard. Like I said, I have used this drive and the disk images on other Macs running different systems up to 10.11. This was my first attempt at using them with 10.13.

And, as Uncle Steve used to say - there's just one more thing...

I don't know if this matters at all, but the iMac i migrated from was running Snow Leopard Server. I did not install Server on the 10.13 system.

I thank you in advance for any help you may be able to offer!