# Different errors

Hi, im new to sage, but i like it. (i Have some expertise with mathematica, but not with sage).

I created a notebook on the uw.sagenb.org server. It contains the text: http://typewith.me/jmSO3JENxg

Sometimes a I get the error: Traceback (click to the left of this block for traceback) ... TypeError: 'sage.symbolic.expression.Expression' object is not iterable

Full error here: http://rn0.ru/show/1422/

If I want to use latex, in the second lowest field, i get an error: sh: dvipng: not found Full error here: http://rn0.ru/show/1421/

Somehow, the fields work sometimes, and sometimes they dont... I have the feeling I would need to "quit the kernel" like in mathematica, from time to time...

Does anyone know the errors?