so how its possible that the new post gallery overwrite the old post code ?
This should not be possible at all. Each time a new gallery is created (via the 'Add Juicebox Gallery' button), a unique gallery id is generated.
There should never be two gallery shortcodes with the same gallery id.
Also, gallery ids should be interchanged manually and gallery shortcodes should not be copied and pasted between posts.
Unless someone has manually changed a gallery id in a gallery shortcode (or has copied and pasted an existing shortcode), I cannot explain why you have duplicate gallery ids.
Also, there is no way for a gallery id (or gallery shortcode) to change by itself (unless you have a schedulted task on your server or WordPress site which is somehow interfering with post content).
A gallery id signifies which configuration file (stored in the 'uploads/juicebox/' directory) should be used.
Inside the configuration file is a post id which then tells the gallery which post's attachments to display.
If you check out your 'equis-bar-grand-opening' gallery, you'll see that it uses a gallery id of 208.
If you then examine the contents of the http://www.rivieraevents.com/wp-content … ox/208.xml file, you'll see that the corresponding post id is 5354. Therefore, the gallery is displaying all images attached to post 5354.
If you were to copy and paste a gallery short code (complete with gallery id) to a different post and click 'Update' (which I would not recommend), then the post id in the corresponding configuration file will change (to that of the current post) and the gallery will display the images attached to the updated post id.
I really do not know what is at the root of your problem but maybe my notes above will help to clarify some things.