Hi Joe,
As far as I know, the problem should be reproduced only if you are trying to assign the WOL tickle task to the collection which contains inactive clients (i.e. at least some client has Symantec Management Agent uninstalled). If you create the new task and add only active clients then this problem should not happen. Is it your case?
Also, are you trying to WOL windows clients or ULM clients?
Thank you,
Alex.