I just completed the update and I am having the exact same problem. Any resolution from Sage yet? Right now I am on ignore waiting for help.

Please call support at 1-800-551-8307 for assistance on this. Installing the YE update should not cause the files to no longer be accessible from a workstation.

I was holding when I posted this message. The fix was amazingly simple. The version number stored on the server in an xml file was wrong. I don't know how I could have created this situation by running the updates but once the tech had me change the version number on the server the problem was resolved.