You are getting this email because one of the Extract Transformation and Load (ETL) jobs has failed during the run.
You can see the etl.log for more details to find out the reason for the job failure.
If the ETL job failure is happening for the first time, you can restart the ETL ([RUNTIME_DIR]/scripts/collabnet restart etl) and check if the problem is occurring again. You can increase the JVM heap size by specifying the same in ETL_JAVA_OPTS if the problem keeps recurring. The default value is -Xms160m -Xmx256m. You can increase the heap size depending on the memory available in the box.
Check if both TeamForge and Datamart are up and responding to queries if there is no response from the database. Restart the ETL ([RUNTIME_DIR]/scripts/collabnet restart etl).
Contact CollabNet support if the problem persists.