Hello Mogul,
Sorry for the trouble here!
Just to confirm, are you using any caching plugins on your site? I’ve seen this sort of thing pop up before and it was due to a caching plugin that was minifying the calendar’s scripts in a way that caused Javascript errors much like this. If that’s the case, then please empty the cache and disable the plugin to see if that makes a difference.
If that’s not the case, then will you please follow the steps outlined in this post and let me know if you noticed a difference when the site is in default WordPress conditions? This will help us determine if there is a conflict with perhaps the theme or another installed plugin and, if so, where it is.
Thanks!
Geoff