I solved the problem this way: in the method _set_image_to_view() add the line _disable_keyboard_navigation(); between lines _resize_container_image_box(objImagePreloader.width,objImagePreloader.height);
and
objImagePreloader.onload=function(){};
Thus the entire method is as follows:
function _set_image_to_view() { // show the loading // Show the loading $('#lightbox-loading').show(); if ( settings.fixedNavigation ) { $('#lightbox-image,#lightbox-container-image-data-box,#lightbox-image-details-currentNumber').hide(); } else { // Hide some elements $('#lightbox-image,#lightbox-nav,#lightbox-nav-btnPrev,#lightbox-nav-btnNext,#lightbox-container-image-data-box,#lightbox-image-details-currentNumber').hide(); } // Image preload process var objImagePreloader = new Image(); objImagePreloader.onload = function() { $('#lightbox-image').attr('src',settings.imageArray[settings.activeImage][0]); // Perfomance an effect in the image container resizing it _resize_container_image_box(objImagePreloader.width,objImagePreloader.height); // for reducing problem with navigation using keyboard (switching some pic at one time) _disable_keyboard_navigation(); // clear onLoad, IE behaves irratically with animated gifs otherwise objImagePreloader.onload=function(){}; }; objImagePreloader.src = settings.imageArray[settings.activeImage][0]; };