The PowerPivot addin for Excel is used to create a PowerPivot model using SQL Server as a data source and the user manually uses the Excel connections screen to have the password be saved.
Later when the PowerPivot addin is used to change the model, like by changing some query text the model will fail to refresh.
The model command text gets out of sync with what Excel has for the command text. This is a known issue and may not be resolved anytime soon.
Using SQL Server authentication is not recommended for many reasons, Windows authentication to the SQL database is the recommended authentication mode.
Storing a login ID and password to a database is exceptionally insecure and a not recommended. As the workbook gets passed around the password is visible to anyone who opens the workbook.
If you must use SQL authentication, it can be done in a much more secure way if you have SharePoint and PowerPivot for SharePoint.
- Create the workbook with Excel same as before, but never check to "Save Password", you will be prompted whenever the password is needed.
- Upload the file to a SharePoint PowerPivot Gallery document library
- In the Gallery click the "Manage Data Refresh" button
- Configure a schedule to refresh the data, you can put the SQL userid and password in the schedule, these values are never readable by users
- Have users use the workbook
The above method is vastly superior to saving the password in the workbook. At no time is the password visible to a anyone, only the workbook author needs to know the password. The data is only refreshed once per day or whatever interval is set in the schedule. This is a large performance gain. Without scheduled data refresh, the data refresh processes might be done by every user that opens the workbook multiple times, with scheduled data refresh it only happens once per time period.