@yogeshpunia66, Is it for Calendar Custom Visualization App or Calendar Heatmap Custom Visualization?
As per the App details Calendar Custom Visualization App is supported on Splunk Enterprise 6.5 onward. There was a change in Custom Visualization API between Splunk version 6.4 and 6.5. Maybe because of the same the App is not working on 6.4.4.
I dont think so. But you should contact the app's developer.
6.4 released 1st version of Custom Visualization which was modified considerably in 6.5 and till now same version is being used. I am not sure whether the developer would/had gone back to create app for 6.4 as well.
@niketnilay is correct in that the Calendar Custom Visualization is only compatible with Splunk 6.5 and above. However, this visualization was based off of some work that will work with version prior to 6.5. Here is a blog post explains how -> https://www.splunk.com/blog/2013/10/14/calendar-custom-visualization-with-simple-xml.html