Problema para recorrer array multidimensional

[Montes28]

tengo el siguiente array multidimensional

Código PHP:

array:10 [▼
  "cam1" => array:2 [▼
    "file" => "/var/www/html/repositorio/cam1/image20151112165953.jpg"
    "time" => 5
  ]
  "cam1" => array:2 [▼
    "file" => "/var/www/html/repositorio/cam2/image20151006235908M.jpg"
    "time" => 52856
  ]
  "cam1" => array:2 [▼
    "file" => "/var/www/html/repositorio/cam3/image20151112170052M.jpg"
    "time" => 3
  ]
]
 

Código PHP:

<?php
@foreach($ultimos as $key => $ultima)
 
    <strong>{{ $key }}:</strong> 
            @foreach($ultima as $k => $u)
 
            <?php echo $u['file']; ?>
 
            @endforeach
            <br>
    @endforeach
?>
 

obtengo este error ErrorException in line 49: Illegal string offset 'file'

si hago un echo $u

Código PHP:

@foreach($lastFiles as $key => $ultima)
 
    <strong>{{ $key }}:</strong> 
            @foreach($ultima as $k => $u)
 
            <?php //echo $u['file']; ?>
            <?php echo $u ?>
 
            @endforeach
            <br>
    @endforeach
 

cam1: /var/www/html/repositorio/cam1/image20151112172007.jpg 5
cam2: /var/www/html/repositorio/cam2/image20151006235908.jpg 52877
cam3: /var/www/html/repositorio/cam3/image20151112172152.jpg 3
cam4: /var/www/html/repositorio/cam4/image20151112172257.jpg 4
cam5: 24122775
cam6: 24122775
cam7: /var/www/html/repositorio/cam7/image20151112172109M.jpg 5
cam8: /var/www/html/repositorio/cam8/image20151112172105M.jpg 4
cam9: /var/www/html/repositorio/cam9/image20151112171746M.jpg 4
cam10: /var/www/html/repositorio/cam10/image20151112172057M.jpg 5