If you used LOE previously (previous builds from last events ever)... you need to delete the LOE data the is created in you own windows account profile.
To get there, on any windows vista/7/8/8.1/10, do the following:
Navigate to COMPUTER, then into the C: drive
Then you go into Users and then into the folder that should be named the same as your current account, most people are likely to only have 2 folders listed, one will be public, the other should be your account folder
Once inside your account folder, in the upper part of the window should be the "address" bar which if you click at the end of it, you can type more to it.... so type the following:
/appdata/LOCALLOWthen hit enter
Once inside this folder, you should see a folder called LoE among others, select it, and DELETE it, make certain you do not currently have the game up and running, once this folder is deleted, fire up LOE and attempt to play
If you do the above, it basically wipes potentially incompatible settings and previous saved data that would not match up with the new build of client. Would be nice if they included a quick excutable that you can run at any time that just deletes the LoE folder that is created in locallow.