I was in the Project->Organize All Workspaces dialog, selected lots of old projects that were ported from V18 but didn't exist, clicked delete and it deleted about 5 of them and came up with a slickC stack.
Invalid argument
wman.ex 4970 wman:SetDescription(6,\n) p_window_id: 39 p_object: OI_TREE_VIEW p_name: ctltree1
wman.ex 4149 wman:SaveDescriptionText() p_window_id: 39 p_object: OI_TREE_VIEW p_name: ctltree1
wman.ex 3996 _workspace_organize_form.ctltree1.on_change(10,7,0) p_window_id: 39 p_object: OI_TREE_VIEW p_name: ctltree1
wman.ex 7280 wman:MaybeDeleteWorkspaceFromTree(6,15,0) p_window_id: 39 p_object: OI_TREE_VIEW p_name: ctltree1
wman.ex 6704 wman:DeleteButton() p_window_id: 180 p_object: OI_COMMAND_BUTTON p_name: ctldelete
wman.ex 6407 _workspace_organize_form.ctldelete.lbutton_up() p_window_id: 39 p_object: OI_TREE_VIEW p_name: ctltree1
dlgeditv.ex 6982 show(-modal -xy _workspace_organize_form) p_window_id: 5 p_object: OI_FORM p_name:
wman.ex 920 workspace_organize() p_window_id: 5 p_object: OI_FORM p_name: