- Has the Algebra filter been activated? (Site administration -> Modules -> Filters -> Algebra Notation "eye" open)
- Did you surround the expression by double @-signs?
- Can you get any Algebra expressions to render?
- Does TeX work? (you can use the same expression, but surrounded by double $-signs)
If the expression is rendered by http://yoursite/filter/algebra/algebradebug.php, then I would assume that all the needed packages must already be installed. Other things to check: