We are currently experiencing issues with group calendar, due to the fact people are using so many different versions, and the latest fix which is meant to fix quite a few sync bugs is not compatible with previous versions.
Please download the latest version from the below link:
It is also advisable to go into you configuration folders on your computer and delete any saved variable files from your computer, so you are effectively starting from scratch.
Please ask for advice if you are not quite sure how do this.
