I have a very weird and specific problem on more than one website (and on more than one host) to which I couldn't find a solution.
SigPro galleries for k2 work in most cases except one:
If you go to Components > K2 > Items and you create an item (without gallery, without uploading any pics etc) and then you go to Components > Simple Image Gallery Pro > K2 galleries and choose to create new gallery for this K2 item and put some pics in it and then go to the k2 item in backend you don't see the images.
The K2 item gives the following error: "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/"
For some reason it doesn't look in media/k2/galleries/hisID for the images but only in media/k2/galleries/.
BUT if you then add more images to that gallery from the item itself, now it sees the images those uploaded from it AND those uploaded from the SigPro component.
(No matter if it sees them in the backend or not, they show in the front-end, just the problem is them not being seen in the item backend when the gallery for the item is created through the sigpro component not through the item)
Also while researching the problem I've noticed that SigPro in Info and Plugins says:
K2 - Simple Image Gallery PRO Not installed- Disabled
But the plugin is enabled and I don't have any version of Simple Image Gallery Free installed, never had.
On one of the hosts and site I have this problem (well on localhost) my whole /var/www is recursively 777 even before k2 and sig pro got installed so I don't think permissions are the problem.