When Sage called me back an hour later, I went to show him the issue, and lo and behold, no error - it just finished the conversion. Apparently, another analyst took another call reporting the exact same issue about the same time I opened my case. Theory is that perhaps Sage Exchange couldn't communicate w/ the ""Vault"" at that time. Ronnie Aspe was who I was working with, and he said he'd check in w/ Sage Payment Solutions to see if there was an interruption in service. I'll follow up on that.
I also got an education on how to install Sage Exchange if it somehow doesn't install as part of WKSETUP (i.e. you don't see the SE icon in the system tray):
1. if you access any place in MAS that requires accessing CC data, it will get installed automatically (I think - either that or it prompts you first).
2. There are 2 components required for SE: The Module SDK and Sage Exchange itself. You should see them both in Control Panel\Programs. If they aren't present, you can manually install them from the 2013 install ""DVD"" by navigating in WIndows Explorer to the folder \Prerequisites\SageExchange\setup.msi to install the SDK, and \BARESETUP\SageExchange.application to launch the SageExchange installer.
Note: you can also launch the SDK from inside the WKSETUP\Prerequisites folder. But the SageExchange installer is not located there. You can also launch the SDK from the installer program for Sage 100 under Productivity Applications.