Below error message appear when loading basket in SAP Download Manager.
SAP has 2 different type of user id.
1) S-ID : Traditional SAP Logon ID
2) UID : Universal SAP Logon ID
For loading basket in SAP Download Manager, it requires the traditional S-ID. Even if the password may be correct, please follow below steps to resolve the authentication issue.
Step 1 - Go to the SAP Universal ID Account Manager, log on with your SAP Universal ID credentials
Step 2 - Select the linked S-user ID you would like to modify
Step 3 - Click the pencil icon to edit the "Reset Account Password" card
Type in your new preferred account password according to the listed criteria
Repeat the same password
Click Save
Step 4 - Return to the application where you faced the error of invalid credentials and use the S-User ID and your newly set account password to log on.
Reference