The definition of these alerts are:
Monitoring error (SQL Server data collection)
One of the following conditions applies continuously for 2 minutes:
Problems with WMI
Problems with the remote registry
File sharing issues
SQL connectivity issues
Monitoring stopped (host machine credentials)
SQL Monitor is unable to collect monitoring data from the host machine because the credentials supplied to connect to the machine are invalid or lack permissions.
In the case of the first alert, once the condition which caused it to be generated are no longer present the alert will change from Active to Ended. So it looks like you have a problem with the Windows Management Instrumentation protocol which SQL Monitor uses to collect some data from the monitored host machine. Please take a look at the document links which are listed in this document towards the end of the section marked Testing WMI.
The second alert can be a little more difficult to pinpoint. How long does it stay active for? how often does it occur?
Technical Support Engineer