In visual studio 2008 (SP1 applied) there appears to be a bug in the state workflow designer tool.
On adding a HandleExternalEvent activity and setting the Interface type to that of an interface in a reference assembly with the same prefixed namespace (eg XX.Core.Contracts as the namespace of the interface containing assembly and XX.StateWorkflowLibrary as the namespace of the workflow) , on trying to reload the designer it will fail with the message "Could not find type ''...." yet it will build and run fine. If the prefixes of the associated namespaces are different then no issues.
NB a workaround is to create a local interface and implement the referenced interface - this works fine.
Anyone know of a hotfix for this designer issue?