DB4 complaining about lockers?

[RJ45]

Hello I haev lately this error mesage always the same time of day once a
day:
imaplog:Feb  7 04:00:00 venus ctl_deliver[429]: [ID 866726 local6.warning]
DBERROR db4: 6 lockers
imaplog:Feb  9 04:00:00 venus ctl_deliver[3062]: [ID 866726
local6.warning] DBERROR db4: 4 lockers
imaplog:Feb 15 04:00:00 venus ctl_deliver[10431]: [ID 866726
local6.warning] DBERROR db4: 4 lockers
imaplog:Feb 18 04:00:00 venus tls_prune[29008]: [ID 866726 local6.warning]
DBERROR db4: 4 lockers

I have cyrus-imapd-2.1.12 and cyrus-sasl-2.1.12 compiled with db4.1.25
anyone experiened this problem? 

thanks

Rick