Ok, I have exhausted my research on this problem.

Joomla 1.5.22
K2 v. 2.5.4
Sig Pro 2.5.7

Had it installed and working. no problem.

didnt need to use it for awhile. went to upload a new image gallery. didnt work. just went back to home screen.

checked permissions - cache,media,k2, galleries directories all 777

went to previous article that was previously working. got this 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/384


hmm. front end just has tags where gallery should be.
{gallery}384{/gallery}

FTP in - media/k2/galleries/384 exists and still has images in it. (worked for undisclosed amount of time just fine)

uninstalled SigPro, reinstalled SigPro.

checked plugin - enabled. default folder - images/stories

here is where it gets weird...

cleared browser cache refreshed page (previously working) - same error - referring to "media/k2/galleries" directory.

that parameter is not set that way anywhere (it is set to images/stories)! not in the database, not in the plugin setting, not anywhere in K2 that I can see... I switch parameter to media/k2/galleries, I get same exact result.

why is it looking in that directory? A directory it shouldnt be looking in(media/k2/galleries), and furthermore, why does it say the directory isnt there when I can see it..

no weird file names or folders in zip file... keep in mind it WAS working fine... I dont know what, when or why it stopped.

I have seen this problem in the forums, but it was cache permissions or someone zipped a folder into their zip file...

not here.. again it was working fine. everything is set proper. and no matter what default directory I set in the plugin, it continues to look in media/k2/galleries... and it acts like the plugin is disabled in the front end ( {gallery}384{/gallery} )

this one has me stumped. that doesnt happen often lol.

First of all:
-upgrade to joomla 1.5.26
-iinstall Admin Tools from www.akeebabackup.com/ in order to fix your permissions as they should be and then reinstall SIG PRO.
-upgrade to K2 2.5.7

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.