Problema di parentesi

Ma comunque ho il seguente errore!!

Balancing year 2007 (Country Congo )**********
[1] 2
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[1] 3
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[1] 4
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[1] 5
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[1] 6
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[1] 7
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[1] 8
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[1] 9
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[1] 10
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[1] 11
Balancing year 2008 (Country Congo )**********
[1] 2
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[1] 3
**********
[1] 4
**********
[1] 5
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[1] 6
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[1] 7
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[1] 8
**********
[1] 9
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[1] 10
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[1] 11
Errore in res[[yearOld]]$bestTab : 
  $ operator not defined for this S4 class