Spoorthy- There can be many reasons. What's the database you're connecting to create the extract? How long has the extract been running before it's timing out? How much data are you loading? If there is a certain time limit set on queries to run on the database, then contact your DBA.
I am using the Microsoft excel CSV file. Which is 657MB size.
Spoorthy- What version of Tableau are you on? Both Tableau Desktop and MS Office should be 64-bit.
I found a similar thread,
Hope this helps.