The cause of an error code of 2147954430 from a web application transaction monitor can be difficult to determine, especially as it’s often intermittent. In my case, investigating the watcher node revealed that too many long-running calls had been included in the monitor and this had caused a backlog on the node, as described by event ID 10503 in the Operations Manager log:
The HTTP URL Monitoring Module detected that a backlog of processing has happened. It might be an indication of too many URL monitors configured for this watcher node.
The solution was to increase the interval between executions of the monitor to one that more realistically reflected the likely execution time. And it might be useful to create a rule to raise alerts from these events on the watcher nodes.