I don't usually use the WebGUI not he OmniSwitches but I've found that after upgrading a standalone OS6860E-P48 to 8.8.152 R01 the web GUI is in a hung state, the initial page starts to come through but then "Requested failed. Request failed with status code 401" error. Checked the swlogs can't see anything obvious no mention of web services failing.
Can we get the output of your "show configuration snapshot"? Also what version did you upgrade from and did you do a direct upgrade or did you do the recommended incremental upgrade? i.e. 8.5 to 8.6 to 8.7 it would be helpful to know these things in order to start assisting.