What's with this bit of EWC funkyness?
I happened upon this post
and was struck by the update: "*Update* - I was able to get this resolved. I didn't have to actually select the account that I wanted to link to. I just selected the 'Link to existing account' option without selecting an account in the list."
The issue here is that Quicken wasn't presenting the Account to link to in the setup process, but blindly clicking "Link to existing account" worked.
The reason this struck a chord with me is that I noticed the same thing when EWC hosed my file
but was too focused on getting my heart beating and getting my file fixed to bother to report this "feature." I've also seen other posts in here mentioning the same thing for EWC-connected Accounts.
Who designs this stuff? You pretty much have to stumble into the "right answer" here either by shear luck or desperation