This error is raised by PDG when Python code attempts to make an invalid work item attribute access. Typical causes are attempting to delete an attribute while the graph is cooking, create an attribute with the same name as an existing attribute of a different type, or setting a value on an attribute that was marked as read only.
Houdini 20.5 Executing tasks with PDG/TOPs pdg
pdg.AttribError class
Generic exception raised when an error occurs when accessing work item attributes