I am getting the following error message after uploading a zip file in the image gallery tab in K2:

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: media/k2/galleries/24

In the plugin settings I have the root folder for image galleries set to: media/k2/galleries

Can someone let me know what I'm doing wrong?

Make sure that you have both k2 and SIG PRO latest versions.
If the problem remains pm me access to backend please.

This error is because you upload the images .zip in K2 before configuring the plugin
Root folder for image galleries -> media/k2/galleries
If you do not do this before you will have error
To correct go to the image folder on the server: root/media/k2/galleries -> delete image folder you uploaded
Then go to the item you have upload image on k2, click on Image gallery tab, click in check-box for delete and click apply or save
Now upload zip image forder and save. That is it.

@tonicosta,
not always. This may be the solution in some cases.