Create a .twbx with Tableau Server data sources
If the workbook contains connections to a published Tableau Server data source, you must download a local copy of the Tableau Server data source, take an extract of it, and then replace the connection to the local copy for it to be included in a packaged workbook (.twbx).
In the workbook, right-click the published data source in the Data pane, and then select Create Local Copy.
A copy of the published data source is added to the Data pane.
Right-click the local copy, and select Extract Data.
In the Extract Data dialog box, click the Extract button to extract all data from the data source. Creating an extract of the data source allows the person you are sharing the workbook with to have access to a copy of the data source.
In the Data pane, right-click the published data source, and then select Replace Data Source.
Verify that the published data source will be replaced by the local data source, and then click OK.
Right-click the published data source, and then click Close.
Select File > Save As.
From the Save as type drop-down menu, select Tableau Packaged Workbook (*.twbx). After the local copy and extract of the local copy is created and the packaged workbook saved, you can send your workbook.
After I posted this I got to thinking, did you receive a packaged workbook from someone else? Or are you trying to create a packaged workbook and getting this error when testing it?
Getting this error when I package and also when somebody sends to me.