Fatal error: Class 'Model' not found After Upgrade to version 2.0

[eluser]Ali Fattahi[/eluser]
Thanks a lot
after solving this problem i have another problem
i got 3 errors :

A PHP Error was encountered

Severity: Warning

Message: Illegal offset type in isset or empty

Filename: core/Loader.php

Line Number: 81

A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\SabaPay_CI2\system\core\Exceptions.php:171)

Filename: core/Common.php

Line Number: 428
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An Error Was Encountered

Unable to load the requested class: validation
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