I was able to resolve this.
The solution that worked for me was to find the activation.dat file in the Library/Application Support/Adobe/Digital Editions folder and drag it to the Trash. Then I was able to deauthorize the computer in ADE (either Help>Erase Authorization or Command-Shift-D while ADE is open) and reauthorize computer ( Help>Erase Authorize Computer).
General comment to Adobe: Your customers do change computers. EVERY Adobe program (Lightroom CC, Photoshop CC and ADE) was a PITA to bring up on the new machine. Adobe is the worst; almost all other programs came up with little or no problem; at the worst reentry of a serial number of password. Only Adobe required IT technical support, digging around in the Library folder, and trips to the forum.
I wasn't able to find the activation.dat file in the location you mentioned but I did find it in /Users/<user>/Library/Application Support/Adobe/Digital Editions and moving it to Trash and reauthorizing my computer fixed this error. Thanks for the pointer to the trick, rjrose. Error getting License. License Server Communication Problem: E_ACT_NOT_READY