title: SQLSTATE[21000]: Cardinality violation: When product in more than one category - Magento
body: <p>I've been battling with this for a while.</p>
  
  <p>I get a cardinality violation when adding a product to cart that is in more than one catergory.</p>
  
  <p>SQLSTATE[21000]: Cardinality violation: 1241 Operand should contain 1 column(s)</p>
  
  <p>Anybody come across this?</p>