I am trying to release an app from Xcode but as soon as I try uploading to the app store or exporting in any fashion, once it checks for signing from iTunes Connect, I receive the error
Your session has expired. Please log in.
I have made sure that I can log into my account on iTunes Connect and the signing certificates and provisioning profiles are current from the developer center.
I came across a similar issue last week: Xcode 6.4 Export Adhoc "Session has expired" but this issue seems different. I am using Xcode 7.1 this time, so the crash that I was observing last week may indicate the problem is different.
The session of one of my accounts (not even the one I was trying to use) had its session expired. This seems to be new. I just had to re-sign in to the errant account in Xcode > Preferences > Accounts.