Notification Services failed to get a list of the match ru..

I have a custom event provider. In the last two days I've
received this error message for two differents events:

Notification Services failed to get a list of the match
rules.
SqlServerError:
  Source: .Net SqlClient Data Provider
  Number: -2
  State: 0
  Class: 10
  Server:
  Message: Timeout expired. The timeout period
elapsed prior to completion of the operation or the
server is not responding.
  Procedure: ConnectionRead (recv()).
  Line Number: 0

at
Microsoft.SqlServer.NotificationServices.Common.RuleEnumer
ation.InitRulesEnumeration(SqlCommand sqlCommand)
at
Microsoft.SqlServer.NotificationServices.Common.RuleEnumer
ation.InitEventChronicleRulesEnumeration(Int32
eventClassId)
at
Microsoft.SqlServer.NotificationServices.EventClass.get_Ev
entChronicleRuleEnumeration()
at
Microsoft.SqlServer.NotificationServices.EventClass..ctor
(NSApplication nsApplication, Int32 eventClassId,
SqlString eventClassName, String fileGroup)
at
Microsoft.SqlServer.NotificationServices.EventClassEnumera
tion.Initialize(NSApplication nsApplication,
SqlConnection sqlConnection)
at
Microsoft.SqlServer.NotificationServices.EventClassEnumera
tion.Initialize(NSApplication nsApplication)
at
Microsoft.SqlServer.NotificationServices.NSApplication.get
_EventClassEnumeration()
at
Microsoft.SqlServer.NotificationServices.Event.Initialize
(NSApplication nsApplication, String eventClassName)

any idea?<!-- ~MESSAGE_AFTER~ -->