Thumbnail is not displayed!

as shown in the screen print, the event thumbnail does not appear from the xibo admin interface and when I click on it, I get the following error message:
Failed to load image: index.php? P = module & mod = image & q = Exec & method = GetResource & mediaid = 143

Do you have any idea about the origin of this pronblem and how do I fix it?
The xibo server is under version 1.7.9 and my clients are in version 1.7.6 and 1.7.5

Thank you in advance for your precious help
best regards

I’d double check if you have fully qualified path to the CMS library in CMS settings
and perhaps that mediaId 143 exists in the library as well.