This situation could be caused by a few problems:
1) Check that the database indicated in the DBID.xml actually exists in the specified database server AND that you can login/access it with the ''td'' user or Win-auth user (SQL-Server) or in Oracle the schema/user with the same name as the project database (schema).
2) Make sure (with a sample working project's DBID.XML file) that the DB Connect string and DB-Server name are correct
3) Generally, when using SQL-Server with SQL-Server-Authentication, or Oracle, the password is the same for all of the QC schemas/databases. There is an encnryped password string in the DBID.xml file for the project - check it against a working project's DBID.xml file.
4) Check the project repository folder indicated in the DBID.xml file. does it exist?
5) if using SQL-Server with SQL-Server-authentication, AND the project DB was RESTORED into SQL-Server from backup, did the DBA run the sp_change_users_Login command to ''fix'' the ''td'' user?