On Website I run K2 und SimpleImageGalery Pro.
So far everything worked fine.
But since a few days I have serious problems. Whenever I or someone else tries to read an artikle that has a gallery or video you get the following error messages:

JFolder: :files: Der Pfad ist kein Verzeichnis! Pfad:

and

There was a problem rendering your image gallery. Please make sure that the folder you are using in the Simple Image Gallery Pro plugin tags exists and contains valid image files. The plugin could not locate the folder:

The gallery or the video are still displayed, but the text is no longer visible. Instead you get to see this:

{gallery}759{/gallery}

Why is that and how can I fix this?

Hello,

Since this is related to a commercial extension. please post this issue on the helpdesk so we can troubleshoot the issue.
Furthermore post a link and credentials for your site.