We have an article on this error message here: Data Engine Error 4: File Used by Other Process | Tableau Software
Basically, the extract file is in use by some other user while you are attempting to make those changes. "Another Tableau Desktop session is open at the same time and connected to the extract (*.tde) file. The existing session has a lock on the file, so you are unable to perform the refresh from a different Tableau Desktop session."
If this issue still crops up after addressing the solutions in the article linked above, you may want to reach out to Tableau Technical Support: http://www.tableau.com/support/request
Hope this helps!