Same here. I can't delete an unused group, and I receive various server error messages when I try. I need to reclaim file storage from that group but can't delete items in the library that are stored on the Zotero server, either. Even though I deleted all items and attachments in the desktop Zotero client, the changes won't sync to the server (no errors, the deletions just don't sync). If I try to delete items through the web library interface, nothing happens (using the trashcan button).
I feel like an idiot. I can't find a way to delete my empty groups either on the desktop client (most recent build) or the web client. I read the documentation but couldn't find an answer. A couple of posts mention a "delete" button. I can't find that. Any help would be appreciated.
No confirmation screen after trying to delete, just an error.