Treemap Chart not showing on Server

Hi,

I ran into an "Unexpected error occurred; contact your system administrator" error when I try to use the Treemap in my Dashboard. The treemap looks fine in Design Studio, but when I run it locally or on the server, the error occurs. The error message displayed is " Object doesn't support property or method 'toUpperCase'.

Has anyone else experienced this error before?

Any help would be much appreciated. Thanks in advance.