Hi Ashish,
These issues could have many potential root causes, this is why as much details as possible will be needed to find the root cause.
It is possible to start investigation with the get-viaccount alone:
vSphere 6.0 Documentation Center
Please try:
get-viaccount –Domain “yourdomain”
get-viaccount –name “yourdomain\oneuser”
get-viaccount –name “oneuser”
Is it a large active directory domain? If it is the case then some potential root causes:
vCenter Settings>Active Directory settings. Maybe needed to increase the Active Directory Timeout or Disable the Query Limit.
Single Sign-on>Configuration>Identity Sources: “yourdomainname” identity source. If you are not using the Active Directory (Integrated Windows Authentication) maybe reduce the scope of the AD query by being closer to the “OU” containing your VMware yourdomain\users and test the connection. Ensure that the account has also enough rights to browse the domain.
In the same place check that “yourdomain” identity source is the default.