The gallery worked perfectly, and then suddenly stopped. This is the message.

There was a problem rendering your image gallery. Please make sure that the folder you are using in the Simple Image Gallery plugin tags exists and contains valid image files. The plugin could not locate the folder: images/galleries/2014

1) There's only images in the folder.
2) Folder permissions is 755.
3) The plugin is enabled, and referencing correctly.

Hi,

Can you try with a different gallery?

Just uploaded a new gallery with totally different images. It's doing exactly the same thing.

Then it's either a permissions or a setup issue. Ensure that the folder permissions are set to 755 and the file permissions are set to 644. Finally ensure that the path is correct. As the message says the plugin is searching at the folder YOUR_SITE/images/galleries/2014 .

All of a sudden I get the same message. Have used this for years without a problem.
I discovered there is a connection with the number of tags on an item. If an item has more than 4 tags, then I get this error message. I can't understand how the tagging is related to the images though.
site: www.kunstinlochem.nl

@Egbert Oldenboom

I don't see any issues on your site. Page www.kunstinlochem.nl/index.php/kunstroute-2014/kunstwerken/item/346-marianne-mol has more than 4 tags and the gallery works fine.

Well just compare www.kunstinlochem.nl/index.php/kunstroute-2014/kunstroute-2014-locaties/lochem-barchem/item/746-jeannette-van-faassen
With
www.kunstinlochem.nl/index.php/kunstroute-2014/kunstroute-2014-locaties/lochem-barchem/item/512-jeannette-van-faassen
The only difference between the items being the tags. Yet the first has no error, the second does have an error.

OK I think I understand what the problem is. K2 can't handle spaces. I knew this to be a problem with names of images, much to the frustration of my users. But now the inability to handle spaces seems to have stretched itself to tags. A new challenge ;).

I think I jumped to conclusions. I still have the situation with the number of tags giving problems. In the two examples above the one with two tags has no problems, the item with 3 tags gives the error.

It has nothing to do with the tags as i already explained. The issue is raised from the galleries of the related items. Example: www.kunstinlochem.nl/index.php/kunstroute-2014/kunstroute-2014-locaties/lochem-barchem/item/661-astrid-koppen . This means that either you have deleted this item's gallery files from the server or the permissions are not correct.