Lightning Experience cannot be enabled - "Enable" button automatically switches back to "Disabled"
|Knowledge Article Number||000232992|
|Description||When enabling Lightning Experience, if the button switches back to disabled automatically:
This may be due to an invalid State code being used by State & Country Picklists.
|Resolution||To resolve the issue, FIRST try going to "Company Information" in your Setup Menu (Type in "Company Information" in the Quick Find box in Setup).
In the "Address" Section, make sure the State/Province or Country values are official State & Country picklist values. If not, select the correct value from the dropdown picklist:
Next, try to enable Lightning Experience.
If this does not work, you will need to disable State & Country Picklists:
Then, re-enable Lightning Experience in the Setup Menu.
Once Lightning is enabled, users can go back to Data Management > State & Country Picklists, and run through steps 1-5 to enable with valid state/country codes: