Microsoft Account login to CompanyB SharePoint site prevents logging into my company SharePoint site
Hello, One of my users regularly logs into a vendor's SharePoint site using his Microsoft Live account. After closing and logging out of the vendor's site, any time afterward that he tries to log into our company SharePoint or O365 site at portal.office.com, he receives an "incorrect login" message. We use Office 2016 Pro 32-bit desktop apps, and have E3 O365 subscriptions, OneDrive for Business and Sharepoint Online. We also use Multi-Factor authentication for all our accounts. The problem appears to be related to Office 365 single sign on: The credentials dialog URL changes to Live.com instead of remaining on the expected portal.office.com site. I can confirm the sites by URL address: He uses portal.office.com or company.sharepoint.com and the URL is correct until the credentials login appears, then it switches to the Live.com URL. I was able to temporarily able to fix this by clearing his browser cache, but as soon as he logs into the vendor's site, the problem reoccurs. Another work around is to use two web browsers, but we do not want that as a permanent fix. I've gone into Credential manager on his machine. There do not appear any stored Web credentials, but there are lots of Windows credentials, except none of them appear to be related to the websites. Anyone have this problem, or can suggest additional troubleshooting ideas? Thank you!