[Dovecot] Sieve-storage: couldn't find storage root directory

[Asai]

Greetings,

Using Dovecot 2.2.4.  In my DSync logs, I'm getting the error message:

Error: sieve-storage: couldn't find storage root directory; sieve_dir was left 
unconfigured and autodetection failed

However, I have the following configuration set:

plugin {
  sieve = /vmail/%d/%n/sievescript
  sieve_dir = /vmail/%d/%n/
}

Please, if you have a moment, tell me what I'm doing wrong here.

Thank you.

--
--Asai