Can not add action to workflow

After creating a workflow transition, unable to create an associated action.

eg admin/build/workflow/actions/1

Screen blanks, log message.

[04-Apr-2008 09:53:45] PHP Fatal error: Call to undefined function actions_key_lookup() in [...]/modules/workflow/workflow.module on line 1429

Using actions 5.x-2.0.

Should I be using 5.x-1.0?
Sorry if this is a dupe or I'm not using a properly matched version number.