It's difficult to provide a quick reply without seeing what the exact
lines were in the waldorf theme that you have, however, it seems to be that
the theme assumes that the Class 'SAR_Generator' is available by default
and doesn't check if this isn't the case.
I suggest logging in via ftp and finding this section of code in your
functions.php around line 469 and comment this out and possibly other lines
that relate to this.