The following remote response error “Remote response error : Error parsing json response: ‘Unexpected token <‘. Logged in?” is a common error that occurs in a number of scenarios, most commonly:

• When the user is inactive for a period of time and is automatically logged out of Salesforce. Attempting to interact with the calendar will cause a remote response error.
• If the user is logged into Salesforce in two different tabs and logs out on one tab, interacting with the calendar on the other tab will cause a remote response error.

It can be resolved simply by logging back into Salesforce.