Hi Atul -
There are any number of reasons why these errors could be occurring, so (unfortunately) simply posting the error message by itself won't likely allow anyone here to help you.
At a minimum, you'd need to gather and post your logs. Tableau logs are pretty complex and there are lots of them, so I'd suspect you'll be hard pressed to get someone here to dive into them on your behalf. Your best bet is to open a support case with Tableau and send the fine folks @ TECH SUPPORT your logs.