First, you need to avoid a string literal pointing to a directory
You can do this by adding @ in front of the line or by adding a double backslash.
FileUpload1.SaveAs(@"C:\Users\Vinay\Documents\Visual Studio 2010\WebSites\Onlinedoctorsportal\vini" + FileUpload1.FileName);
OR
FileUpload1.SaveAs("C:\\Users\\Vinay\\Documents\\Visual Studio 2010\\WebSites\\Onlinedoctorsportal\\vini" + FileUpload1.FileName);
Secondly, make sure that the user with whom your ASP.NET application pool is working has write permissions to the specified folder.
A quick check to verify that this is the problem is to issue your local administrator account in the web.config file.
You can do this by customizing the impersonation tag as follows:
<identity impersonate="true"
userName="domain\user"
password="password" />