I'm not able to enable offline drive in either the new or old Drive interface.
In the new interface, I select "Offline" > "Sync…" > "Done", and when I open the dialogue again, my settings have have not changed.
In the old interface, I select "Enable Offline" and the page never completes loading, and I get stuck in an endless loop of network requests to:
https://docs.google.com/static/doclist/client/js/2418050222-offline_launcher_i18n_offline_launcher_core.js
304 response
https://docs.google.com/offline/optin?json=1
400 error
Screencast gif here: https://dl.dropboxusercontent.com/u/126030141/Share/offline-drive.gif
Best Answer
This is due to the user being logged in with multiple accounts (which can be checked by clicking on the user profile picture icon on the top right corner of Google Drive). By being signed in with multiple accounts, Google Drive would be clueless about which account to use when accessing
https://docs.google.com/offline/optin?json=1.One simple workaround is to sign out of all accounts and log in with the specific account that you wish to use for Google Drive offline. Please note that this only works for Google Chrome and only one account can have Google Drive offline at any one point (unless using multiple users in Google Chrome).
Note: This is similar to Gmail's Error 400 Bad Request, which has been explained in more detail here.