I live in the Netherlands, and use eM Client 7.1.31849.0.
I get the same error message regarding synchronizing the eM Client calendar with the Outlook calendar, over and over again. Multiple times a day.
Enclosed is a screenshot of that message.
I made no changes in eM client or in my system before the problem started.
I did delete the hotmail account from eM Client, and re-installed it.
I saw this before with Internet Calendars, and when I saw your error, I thought it may be the same.
You might have better luck deleting your account in Em Client and then setting it up as Exchange. Instead of using Automatic Setup, use Mail > Exchange.
It must be something in your calendar that eM Client is unable to read. If you have a Pro License, you could open a support ticket for this. They should be able to discover the problem from your logs.