Hello Fareed Ahmed,
Many things could result in this error. Without more information on what specifically is happening, it is hard to assist here.
Is this a new installation or an upgrade of an existing install that was previously working?
What version of Tableau Server is being used?
Have you upgraded to the latest version and drivers for Tableau Server? Did the issue persist?
If this is a roadblock however, please submit a support case from your customer portal login.
How about restarting the server?