Yep - same issue here and I can not pin it down. MLS and the HAI agent are on the same machine running server 2008. For no reason, outgoing communications get corrupted between the driver and the agent. It is interesting that the communications from the agent to the driver are stable.
Sometimes, just an agent restart fixes the issue, but most times I must restart MLS to get things working. I have tried every combination of the above.
The firewall port is open. When communications fail, I get the same results in that the panel goes into reset and does a "GetVariables" looks to me like the Agent is receiving somthing, but that it is not correct. I do not think that this is a port issue.