When migrating from Exchange 2007,2010,2013 or Office 365 to Exchange 2007,2010,2013 or Office 365 you may see a similar error during the migration:
29/01/2015 09:46:42 The request failed. The remote server returned an error: (401) Unauthorized. The remote server returned an error: (401) Unauthorized. -29/01/2015 09:46:42 Error creating source session. The request failed. The remote server returned an error: (401) Unauthorized.
You will need to Grant Application Impersonation rights for both the source and target Admin accounts. Below is a list of KB articles on how to do so depending on what version of Exchange your are migrating from and too:
Note: ApplicationImpersonation rights may take any where from 30 minutes to 48 hours to take effect. If the ApplicationImpersonation rights still do not take effect, then in some instances the rights may need to be removed and re-applied to take effect.
Please also check the password for the logon account hasn't expired.
If using Azure AD with Conditional Access, ensure that the ODME IP addresses are allowed to connect.