class Descriptor does not exists

[pwtitle]

Fatal error: Uncaught Error: Class 'Google\Protobuf\Internal\Descriptor' not found in /usr/local/php-fcgi/lib/php/Google/Protobuf/Internal/MessageBuilderContext.php:48 Stack trace: #0 /usr/local/php-fcgi/lib/php/Google/Protobuf/Internal/DescriptorPool.php(82): Google\Protobuf\Internal\MessageBuilderContext->__construct('google.protobuf...', 'Google\\Protobuf...', Object(Google\Protobuf\Internal\DescriptorPool)) #1 /usr/local/php-fcgi/lib/php/GPBMetadata/Google/Protobuf/Internal/Descriptor.php(17): Google\Protobuf\Internal\DescriptorPool->addMessage('google.protobuf...', 'Google\\Protobuf...') #2 /usr/local/php-fcgi/lib/php/Google/Protobuf/Internal/FileDescriptorSet.php(31): GPBMetadata\Google\Protobuf\Internal\Descriptor::initOnce() #3 /usr/local/php-fcgi/lib/php/Google/Protobuf/Internal/DescriptorPool.php(60): Google\Protobuf\Internal\FileDescriptorSet->__construct() #4 /data/www/linktour/w/public/GPBMetadata/Linktour.php(21): Google\Protobuf\Internal\DescriptorPool->internalAddGeneratedFile('\na\n\x0Elinktour.pr...') #5 in /usr/local/php-fcgi/lib/php/Google/Protobuf/Internal/MessageBuilderContext.php on line 48