Unsupported operand types in system.module line 2134 when trying to add product with drupal commerce
Either $item, or the return value from the db_query() statement, are resolving as something other than an array. Drupal is expecting them both to be arrays, so you get an error when it unconditionally tries to combine them.

It's not possible to debug something like this without access to the site; I'd recommend stepping through the code with a proper debugging tool to see exactly which side of the equation is failing. 

At a guess, I'd say $item is the problem. You'd expect to see more notices about undefined array indexes if it was simply that $item['path'] was missing or something like that.

One low-tech debugging approach is to temporarily disable custom/contrib modules one by one and see if you can find something responsible.