Deltek and Active Directory both allow for forcing passwords to be changed on a periodic basis, or multiple logins with the wrong credentials can disable accounts.
If you use a connector, you have setup a Service Account in Deltek (and possibly Active Directory) that the connector uses to communicate, and if that password expires or the account is disabled, your system administrator must update the Connector to use the proper credentials.
To do this, log into https://app.blackboxconnector.com
Browse to My Connectors
Click on your Instance's DataSources button you wish to modify, then select the "Deltek" endpoint's data source (you may have more than one - all should be updated).
On the Deltek Authentication area, verify your credentials and click Save
