Cookie 570429 not found, dropping ack

Hi,

we have a problem acknowleging some alerts.

/var/log/xymon/hobbitd.log shows:

2010-03-29 23:23:04 Cookie 570429 not found, dropping ack

.bb 127.0.0.1 "hobbitdboard fields=hostname,color,cookie"

<..> server10.internal.net|green|0 server10.internal.net|red|570429 server10.internal.net|green|-1 server10.internal.net|red|947608 server10.internal.net|green|-1 server10.internal.net|green|-1 <..>

at the same time there is no problem acknowleging alert with cookie 947608 though. could anyone give me some hints how to solve this problem?

p.s. we're running version 4.2.3