The problem is with an external provider which is having sporadic issues with APIs that are tied to this feature. The problem has been escalated and we are working with the teams to get the issue resolved.
if you need a particular image, you can download to their laptop or another device, Then you could manually import to Cisco Catalyst Center.
You have another device with the necessary image in flash. Copy the image from the device to internal server. Then import the image to Cisco Catalyst Center from internal server.
Just wanted to stick my 2 cents in. I am as well, recieving this error. Started a while back, just neglected to pursue it due to the "workaround". But it's effecting other items as well, KGV doesn't download either, but guess what? You can do that manually as well. With TAC, we did notice my Trustpool is empty. and there doesn't seem to be a good way to download the entire bundle, as it only accepts single certs, ie: cer/etc..
Quick edit, I was on various versions... and currently on 126.96.36.199 with the same error