Error clearly said that open workbook in newer version. May be the workbook created or saved with 10.5 and above version.
Just install new version and test it.
I was able to figure out the issue.
I updated to 2018.2 but my files were saved in 10.5
I had two versions of Tableau downloaded and the default version was 10.4 for some reason.
I removed the 10.4 version and the issue was solved.
when we install any version newly then tableau will take default that version. If it works then happy.
Please mark it help or correct and close the thread.