I have tried this and am still getting the same error. I can only assume that the issue has something to do with the Group Name, however I am hardcoding the group name in the Web Request by copying it from the group settings of the group I want to be the owner. UGH! Wish there was an easy way to fix this.
Have you tried just putting the group name there without using any variables to make sure its not the variable value rendering causing the issue?
Are you able to create a test group in Sharepoint, something 1 word and simple like TestGroup and then attempt with that group to see what happens? I remember experiencing something like this before. Can you also try surrounding your current group name in single quotes? It just might help and is worth a shot.
I have tested creating a group with the name test and was able to assign that group as the owner. I have tested surrounding my longer group name in single quotes, however that did not work. If I remove the spaces from the group name, that does work. I'm just not sure yet if that will be acceptable to the site owners. Thank you for all of your help!
You may have to modify the soap directly using the "soap editor" area and inserting the group name surrounded by quotes there. I would give that a shot, but I recall also having issues when groups names have a space and quotes tend to come to the rescue these cases. I think I had to mod the soap directly though to get it to work.