Under Microsoft Windows, applications, services and drivers sometimes perform IPC (inter-process communications) using mailslots. The problem is, there are no well-known tools to sniff/monitor mailslot communications, making it rather difficult to debug.
Mailslot Monitor is the missing piece of the puzzle - it lets you see what data messages are being delivered to the mailslots.
It may be necessary to somehow filter only the mailslot you are interested in. Mailslot Monitor plugins lets you do that by specifing a mailslot name wildcard - you will only see the messages being delivered to the mailslots with matching names.