This article describes the issues with VNQM performance as well as the following error message that shows up in the Data processor logs:
2016-03-09 08:56:44,481 [STP DatabaseProcessing Thread #1568] ERROR SolarWinds.Orion.IpSla.Collector.DAL.CCM.ResultHandler - ccmGateway Table. [Index=449]
System.Data.SqlClient.SqlException (0x80131904): String or binary data would be truncated.
VNQM version 4.2.x
The error is caused by issues with the actual Gateways being monitored in VNQM.