Not receiving messages in Spark

We are using a system monitoring system caleld EventSentry. One of the options that it has is the ability to send notification via Jabber. I have it set up to connect to our server, and it appears to be working except for the following problem.

Their client connects, sends a message and then disconnects. If it attempts to send a message to someone on our server the user, using Trillian or Spark, sees the montioring system user come online and then immediately go offline. The problem is that they never get the message if they are using Spark, and if they are using Trillian, they only rarely see the message. Is there some issue with sending messages if the sender logs on and off quickly?