Edit Bootstrap.ini by right-clicking on Deployment share, select properties, click on rules and click ‘Edit Bootstrap.ini.’
Enter the below details and save the Bootstrap.ini file.
Note: Try to use a local account which has access to MDT Server.
Update the Deployment Share by right-clicking on MDT Deployment share name
Goto WDS and update the old boot image either by deleting or replace the old one.
You will not get the invalid credential message when you run the task sequence.