error trying to create new customer via addList

I'm using php and the php toolkit, I was trying to create 50 new customers via the addList operation.

To do this, I just had a for loop with 50 iterations and had the same customer information for each, except that I changed the email address by using the loop counter...

for($i=1;$i<=50;$i++) {

  ...
  'fname'=> 'testcust',
  'lname'=> 'one',
  'email' => "testcust{$i}@test.com",
  'phone'=> '999-888-7654',
  'addr1' => '555 ORder One Test way',
  'addr2'=> '',
  'city' => 'portland',
  'state' => 'OR',
  ...
}

the code works fine, I know because it works when I'm creating just 1 customer.