Bruce -- I beg to differ. I think the terminal ")" should be moved up to replace the "," before "OR". This requires the first 4 lines to all be true OR the fifth true.

Susan -- The problem with English is that it's not logically exact. When you say AND all other ..., you really mean OR all other.

Consider the English phrase "all companies with a head office in Toronto AND Montreal". This excludes every company since they can only have one head office so it can't be both in Toronto AND in Montreal.
In English, it is understood the phrase to mean "all companies with a head office in Toronto as well as all companies with a head office in Montreal". The "as well as" is a logical OR.

Can you try it this way?

AND(
{Order Complete?} =FALSE(),
{Doc Type} ="O",
{OELine Qty Backordered} >0,
{Cust #} ="TD5775"
)
OR(
{OEHead Salesperson} ="KINGSN"
)