Error : TF14045: The identity 19b7a3e0-b25b-4c48-90a8-813202d6d1b4 is not a recognized identity.
above error comes while connecting to tfs server that's why utility continuously displaying reading and analysis because everytime utility connects to source TFS for fetching total number of change sets and lables it encounters same error.
As per microsoft blogs, people are encountering this type of issue after upgradation/db restore for collection. After this process when user tries to connect tfs, it always throws the same error which you have encountered. Have you done any of the above process for the collection you are trying to migrate? You can refer following thread which contains resolution for same error.
http://social.msdn.microsoft.com/Forums/vstudio/en-US/b67ad1d6-d763-4602-bf14-489a3389a30d/getting-tf14045-the-identity-guid-is-not-a-recognized-identity-after-db-restored?forum=tfsadmin
Let us know in case you won't be able to resolve this with the above information and also in case you have not done any upgradation/db restore procedure. In that case we would like to know your source tfs version and older upgrade history of this instance (If any).