probably corrupted - that is, to prevent duplicate attempts/spamming or malicious use, you've "tripped" the connection once, and now they have to "un-do" the connection here.
Who does that? I have no idea. From their page...

I tried to link accounts, but it would not work. Can I still earn miles? What should I do?
If you have attempted to link your SkyMiles and Lyft accounts, but were unsuccessful, you may still be able to link accounts. If you were unable to link your accounts you should have received an error message. If the error message was related to your SkyMiles account, please contact SkyMiles Account Support by visiting the Delta.com Comment page to submit your claim or to speak to a representative visit the Talk To Us page. If the error message was related to your Lyft account, please contact the Lyft Help Center.