Does this happen on more than one workbook? What version of Tableau Server does your company use? You can find this by logging in to Tableau Server from your browser, clicking on the i icon in the top right of the page and selecting "About Tableau Server".
I found a known issue that involves this error (Error: "TableauException: union: Type mismatch" When Opening a Recently Published Workbook | Tableau Software), but it may not apply in this case if your organization uses a more recent version of Tableau Server, which they likely are since Tableau Desktop 10.1 shouldn't be able to publish to an older version of Tableau Server.
More than likely, you or your Tableau Server Administrator (since we'll probably need server logs) will want to file a Support Case | Tableau Software to help narrow down why this issue is occurring and if it might be another iteration of that known issue I linked above.
I hope this helps!
Thanks for your reply. This error happens on that one workbook only and the server version is 10.1.6
The workbook itself contains many different data tables and dozens of sheets. Not sure what triggers the error. I will probably file a support case.