I had the same issue. Here is my fix from a post above:
Within the Historian\libs\Deformat-2.0 folder was an additional Deformat-2.0 folder. The Deformat-2.0.lua file was in that second folder, not the base folder. I moved that .lua file into the first Deformat-2.0 folder. When I loaded back into WoW Historian did load.
Go into the addon folder. You need to move the deformat-2.0.lua file from within the second folder into the base deformat folder. This should fix your issue.
THXSSSSSSSS that was really Easy :)