This error can be the result of several underying problems.
It is advised to more closely monitor the AppMon Collector dashboard(s), and look for indications of an unhealthy Collector. Such indications could show up as low free memory, excessive number of agents, CPU load, excessive number of loaded classes, etc. AppMon v3.2 comes with a default Collector dashboard. This dashboard can be downloaded from the dynaTrace Community Portal for earlier versions.
Other conditions which can lead to this error, include network problems. It is advised to ensure the network is stable and providing uninterrupted service. Note: The agent and collector components should be colocated and not have WAN-like (high latency, low throughput, unstable) links between them.
If insufficient memory is determined to be the problem, increase the amount of heap allocated to the Collector and restart.
Collector memory can be increased by editing the DT_HOME/collector.ini file, and increasing the -Xmx and -Xms parameter. A value of 1024m is generally sufficient, however under heavy traffic conditions and a large number of connected agents, a larger value may be necessary.