Error: Unable to connect to the remote server or Unable to connect to the remote server Some error occured ( occurred ), Please make sure Source is up running and Run the project again.

Note: If this error is accompanied by  Error "The remote server returned an error: (401) Unauthorized" please see our knowledge base article for "The remote server returned an error: (401) Unauthorized".

If the 401 error is not present the issue could be caused by any of the following:-

The most common cause of this error is a configured parameter preventing the server from accepting the connection from Migration Monster, normally a username or password issue. This error can also be caused by high server load causing the connection to be rejected. 

For Office 365, we have seen this when the Office 365 servers are very busy so if you have time to wait a while , try again outside office hours.

This error can occur when using admin credentials and impersonation has not been configured correctly. If impersonation has been configured correctly you should be able to log in to webmail using the admin account and then switch to the user account without any difficulty.

Throttling can also cause these errors and can be resolved by removing throttling restrictions on the server. We recommend following our procedure for removing throttling restrictions. Please see our FAQ section for "How do i disable throttling on office 365 and Exchange Server "

If still having problems, please raise a helpdesk ticket