Couldn't start DropBox

[get_extra_trace_info failed]
Traceback (most recent call last):
File "dropbox/client/main.pyo", line 823, in boot_error
File "dropbox/client/main.pyo", line 5257, in get_dropbox_path
AttributeError: 'NoneType' object has no attribute 'get_dropbox_path'

Original traceback:

Traceback (most recent call last):
File "dropbox/client/main.pyo", line 5536, in main_startup
File "dropbox/client/main.pyo", line 2030, in run
File "dropbox/client/main.pyo", line 1102, in startup_low
File "dropbox/client/multiaccount/instance_database.pyo", line 759, in __init__
File "dropbox/client/mapreduce.pyo", line 81, in __init__
File "dropbox/client/mapreduce.pyo", line 124, in new_user_key
File "dropbox/keystore/keystore_posix.pyo", line 158, in store_versioned_key
File "dropbox/keystore/keystore_posix.pyo", line 135, in store_key
File "dropbox/keystore/keystore_posix.pyo", line 122, in _save_dict
OSError: [Errno 13] Permission denied