I can no longer add my hotmail account to EMClient.

I can no longer add my hotmail account to EMClient. I get pop-up window with message " We’re unable to complete your request. Unauthorized client.The client does not exist.
Anyone has an idea what is happening ? I have tried more than ten times

Same here with my outlook.com account.

If the hotmail account is set to IMAP and the version you are running is older than v7.2.34959 then take a look at this Reaction to the Outlook.com authentication problem note, which is in fact prominently displayed on the main forum page. Short answer: upgrade to the latest v7.2.35128.0 build.

How many account do  you have setup?  the free ware version will only allow 2.  you can purchase the pro version that will take as many as you would like.  there are instructions on the outlook site to setup the account.  have you enabled IMAP on the outlook account?  try this first.