In some cases, you may experience an issue with the Joomla calendar used in JomSocial that will look distorted, similar to how it is shown below, or it wont work at all, or it will give some unexpected behaviors.
This is typically an error attributed to the Joomla template. To verify this is the case, switch to Joomla's default template and see if the calendar is styled and working properly. If so, then your template will have to be fixed by your template provider.
This error occurs because JomSocial does not control the calendar that is used in Events. Although it seems like it is a JomSocial calendar, since it is loaded on a JomSocial page, you are actually accessing the native Joomla calendar and this calendar is controled exclusively by the Joomla template; hence, why it will most likely work with default Joomla templates. Therefore, the calendar issues are related to your template and your template provider should be able to correct the issue. It will likely affect any other component you use that accesses the native Joomla calendar.