If the problem is intermittent, then the cause is likely to be either web sever or internet connection related.
The code on your pages will remain constant and should be rendered with consistency.
Juicebox will display the "Config XML file not found" error if the XML file cannot be reached in a timely manner.
The fact that the problem is intermittent suggests that a timeout error may be occurring (the time taken to fetch the XML file is too long).
I'm not sure it will help but you could try increasing your PHP set_time_limit directive to ensure that your PHP file has enough time to generate the XML file.
You could also increase your browser's default timeout value to see if this makes a difference. (You might need to do a web search to see if this is possible with your particular browser.) I realise that this will not help others viewing your web site but it might give us some insight into the nature of the problem.
I notice that your gallery's XML file is generated by a PHP file but the configURL (the URL for the PHP file) is first generated by a JavaScript function.
Also, your web page loads files from several different domains and includes approximately 40 external JavaScript files and 30 external CSS files.
I understand that you may need everything for your web site to function correctly but I can't help but think that you might have fewer Juicebox errors if things were simplified a bit.
If you have any plugins which you are not currently using, try deactivating them to prevent their files from being loaded into your page.
Try also deactivating W3 Total Cache and allow all files to be served from your own web server (instead of a Content Delivery Network). I do not know if this will make a difference but it might be worth trying so see what happens.
Another thing you might like to try is to hardcode the path to the PHP file in your gallery's embedding code (to see if there is perhaps a timing issue with the JavaScript function which builds the configURL which might be contributing to the problem).
Change:
configUrl: dsidx.details.GetConfigUrl(),... to:
configUrl: 'http://mrtownhome.net/wp-content/plugins/dsidxpress/client-assist.php?action=GetPhotosXML&pid=147337406',You might need to change this in one of your plugin's source files. I realise that this is not a solution (it will only ever show the images for a single gallery) but it might be interesting to see if it helps with the problem.
Unfortunately, I do not have a solution to your problem and some trial and error might be required but I hope the suggestions above point you in the right direction.