Omeka has encountered an error

Exception

Failed to get resolution of image #26497 ("/var/www/html/omeka/files/thumbnails/56887832fcecd8d1e3d4c7c263577b37.jpg").

exception 'Exception' with message 'Failed to get resolution of image #26497 ("/var/www/html/omeka/files/thumbnails/56887832fcecd8d1e3d4c7c263577b37.jpg").' in /var/www/html/omeka/plugins/UniversalViewer/views/helpers/IiifManifest.php:971
Stack trace:
#0 /var/www/html/omeka/plugins/UniversalViewer/views/helpers/IiifManifest.php(425): UniversalViewer_View_Helper_IiifManifest->_getImageSize(Object(File), 'thumbnail')
#1 /var/www/html/omeka/plugins/UniversalViewer/views/helpers/IiifManifest.php(584): UniversalViewer_View_Helper_IiifManifest->_iiifThumbnail(Object(File))
#2 /var/www/html/omeka/plugins/UniversalViewer/views/helpers/IiifManifest.php(202): UniversalViewer_View_Helper_IiifManifest->_iiifCanvasImage(Object(File), 1073)
#3 /var/www/html/omeka/plugins/UniversalViewer/views/helpers/IiifManifest.php(20): UniversalViewer_View_Helper_IiifManifest->_buildManifestItem(Object(Item))
#4 [internal function]: UniversalViewer_View_Helper_IiifManifest->iiifManifest(Object(Item))
#5 /var/www/html/omeka/application/libraries/Zend/View/Abstract.php(350): call_user_func_array(Array, Array)
#6 /var/www/html/omeka/plugins/UniversalViewer/controllers/PresentationController.php(120): Zend_View_Abstract->__call('iiifManifest', Array)
#7 /var/www/html/omeka/plugins/UniversalViewer/controllers/PresentationController.php(120): Omeka_View->iiifManifest(Object(Item))
#8 /var/www/html/omeka/application/libraries/Zend/Controller/Action.php(516): UniversalViewer_PresentationController->itemAction()
#9 /var/www/html/omeka/application/libraries/Zend/Controller/Dispatcher/Standard.php(308): Zend_Controller_Action->dispatch('itemAction')
#10 /var/www/html/omeka/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#11 /var/www/html/omeka/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(105): Zend_Controller_Front->dispatch()
#12 /var/www/html/omeka/application/libraries/Zend/Application.php(384): Zend_Application_Bootstrap_Bootstrap->run()
#13 /var/www/html/omeka/application/libraries/Omeka/Application.php(77): Zend_Application->run()
#14 /var/www/html/omeka/index.php(23): Omeka_Application->run()
#15 {main}