First- or third-party cookies are blocked by the browser or by privacy plugins such as Disconnect and Ghostery.
MetaShare cannot find the cookie set by “login.microsoftonline.com” and therefore document functions such as upload, create, delete and check in cannot be performed. This can happen if “app.metashare.com” and “login.microsoftonline.com” are in different security zones.
Make sure that first- or third-party cookies are not blocked for login.microsoftonline.com and app.metashare.com.
If “app.metashare.com” or “login.microsoftonline.com” are explicitly added to the “Local Intranet” or the “Trusted sites” security zones they should both be in the same security zone or one in the “Local Intranet” zone and the other in the “Trusted sites” zone. This only applies to Microsoft Edge Legacy. For more information, read this page: Are there any recommended browser settings for MetaShare.
If you still get the same error, try disabling browser extensions.