this is what the doc (Understanding Workspaces and Lead Partitions - Marketo Docs - Product Docs ) says:
To move assets to a new workspace, put them into a folder and drag the folder over to the other workspace.
You can't move a program that contains members from one workspace to another.
Have you tried to put them in folders and move the folders ?
Yep. I'm trying to move folders and getting those error messages. Many others must have had this problem. I don't know why there isn't a Doc on it.