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/87

This is becoming very frustrating! Access is correct. It worked twice, the directory setting was not changed and then I began getting this error. Please help.

Please provide us with a link to your gallery page.

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.