Please try the solution provided in the below KB
Increasing the VMware vSphere Web Client session timeout period (2040626) | VMware KB
Regards
Lokesh
Tried both vsphere client & Web UI ?
There could be multiple reasons for it. Could you please give some more info regarding your setup
1. Is it with Vcenter windows/ appliance.
2. Also is the user id your are trying a part of a big AD group. As in does it work with any other user id belonging to different users in your domain.
GaneshRam asks the questions to OP