It depends entirely on the error message. What's the actual error?
It's most likely you didn't extract the datasource before saving it as a packaged workbook. Just exporting as a packaged workbook isn't enough. I'd extract the source, export as packaged and send again.
The easiest way is to send them a Packaged Workbook (File > Export as Packaged Workbook), which will embed the data source directly in the workbook. They can play with the workbook just fine (it's not read-only), and if they want to use the data source for other things, they can retrieve it from the temporary location where Tableau stores it.
To find where Tableau stored a temporary copy of the file that was embedded in a Packaged workbook:
If there is an extract:
Go to Data > [Name of Data Source] > Extract > Properties.
If there is not an extract (the Extract menu is greyed out):
Go to Data > [Name of Data Source] > Properties.
Thank you both for the help. I have done the " export packaged workbook" and sent it on.
I can now add this to my " things I can now do in Tableau" list.