Hi Margot,
Judging by the error message, the website doesn't work with Safari (rather than Safari not being able to view it).
They are doing some kind of browser version check (/toolbox/incBrowserVersion.asp) and the code they are using is crashing.
If they have a feedback/tech support email address send them a notice.
Until then, as Quang correctly says, you'll need to use another browser like Firefox or Camino.