Has anyone else seen this? Googling it turns up one other instance of this happening that I can find, and the solution (rebinding the 2015 CRM site in IIS to another port) doesn't work for me. All the checks work out fine, but when I got to actually do the upgrade, within a minute I get this error.
Action Microsoft.Crm.Setup.Server.StopWebsiteAction failed. Unknown error (0x80005000).
Thanks all.