My File Doesn't Open After Migration
If the migration completes successfully, with no errors but the file is not open at the end, then it could be that your "file is Insecure".
FileMaker Server can be configured to not allow files that do not have good passwords to be hosted. If your server is setup that way, then you file must have a user name and good password, or it will not stay open. Otto will open the file and signal that it was done, but FileMaker Server will immediately close it again. You can see if this is the problem by looking in the FileMaker Server event logs. If this is the problem the log will show a message that says the the "File Is Insecure" and can't be opened.
Here is how FileMaker defines an "Insecure File"
A secure file ..."must not have a Guest account using the Full Access privilege set, a Full Access account with an empty password, or a Full Access account with the password stored in the database using the File Options dialog box Log in using option. Database files with these types of accounts are insecure."