It seems an issue on your core server, not on the client.
Try to look into "vulscanresults" folder under ManagementSuite (it should be empy) (C:\Program Files(x86)\LANDesk\ManagementSuite\vulscanresults)
Also an IISRESET can help.
And finally you can check this doc: Error: "Failed. Cannot Interpret Data" when running a Patch and Compliance scan