Version 5.5.3 - in the content tab of the Archive task, it appears that the main pane should resolve the variables in the view before you have clicked into it to edit the configuration. It resolves the variable for the file mask, which contains a date variable; but it does not resolve the variable for the path, which contains a user-defined variable - it displays the "error in setvariables" message.
There is no issue with the variable itself; once you have clicked to enter the configuration, and you hover the mouse over the path, it is able to resolve the variable. There are also no error messages when running the task, and the task is performing the file zip normally; the issue is only with viewing the variable from that particular pane.