Ejabberd 2.1.5 Connection issues

Hi,

I'm running ejabberd 2.1.5 with more or less only MUC installed and up to 400 people in the same MUC Room (via HTTP-Bind).
Recently, I ran into some problems regarding connection.
Our users complained about connection loss but I can't really figure out what happens.

Memory is max 413MB used of 2GB (monthly max) and load is 0.08 in 15min average this month (0.13 in 1min max this month), so I don't think that's the problem.

I'm currently looking through the logs but I didn't find anything until now.

Does anyone have the same problems or can tell me how I could figure it out?
Do I need to upgrade to a newer version of ejabberd (I don't really want this, because then I can't use the Debian package from apt anymore).

//Edit:
I'm digging through the logs and see now in the time period where the connection issues happen sometimes the following log:

=INFO REPORT==== 2011-10-10 21:00:38 ===
I(<0.18895.1222>:ejabberd_http_bind:508) : Session timeout. Closing the HTTP bind session: "cc2a05e5af3f502489da119465ada229469b222e"

Could this be a problem? I think so. But how could I resolve it? Would it be better with a newer version or with an external BOSH Module like punjab?

Thank you very much,
Michael