Technical Background:
This issue applies to the following products:
Windows Small Business Server 2011 Essentials, Windows Storage Server 2008 R2 Essentials and Windows Home Server 2011.
The “Alert Evaluation Component” is a component that evaluates the system status against a set of pre-defined rules, and then reports the result to health monitor.
This evaluation is triggered every 30 minutes, rules are under %Programfiles%/Windows Server/Bin/FeatureDefinitions/ on the server and client.
When evaluation fails, the system will throw the "Computer Monitoring Error" warning.

This article provides quick workaround for two known issues that triggered this alert, further resolution and additional cases are still under investigation.

Root Cause:
There are several reasons Alert service will generate “Computer Monitoring Error”, including:

1. Client or Server are missing Powershell execution engine.
2. An alert evaluation component throws unhandled Exception. (That’s the most common cause we have seen)
3. An alert evaluation component can’t find its Feature Definition file that includes the evaluation rules.
4. An alert evaluation component does not report results after a certain time.
When these situation happen, those alerts evaluated by that component will never show up. But other alerts or product features will not be impacted.

This warning could be generated by different reasons, the following sections are already known issues caused “Computer Monitoring Error”.

“Computer Monitoring Error” shows on the Server after updated with Update Rollup 2.

Update, a hotfix is avaialbe for fixing this issue, please check following KB articles for download links

You receive the warning "Computer Monitoring Error" in Windows Storage Server 2008 R2 Essentials after you install Update Rollup 2:
http://support.microsoft.com/kb/2686867
You receive the warning "Computer Monitoring Error" in Windows Home Server 2011 after you install Update Rollup 2:
http://support.microsoft.com/kb/2686857
You receive the warning "Computer Monitoring Error" in Windows Small Business Server 2011 Essentials after you install Update Rollup 2:
http://support.microsoft.com/kb/2685867----------------------------------------------------------------------------------------------------------------------------------------------------

This happened after the system installs Update Rollup 2. You will find the following exceptions in the SharedServiceHost-AlertServiceConfig.log file under %Programdata%\Microsoft\Windows Server\Logs.

120222.003152.9814: NetworkHealthEngine: Exception happened in Microsoft.WindowsServerSolutions.NetworkHealth.Engine.BinaryActionDefinition: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.WindowsServerSolutions.Servicing.Alerts.MacClientUpdateCondition.Run(IActionContext context)

Cause
It is caused by one of the Alert evaluation components – ServicingAlerts.dll, when it tries to evaluate whether there are Mac clients in the network.
It will throw an exception when some machine returns "unknown" for the OS version. It could happen when you have a machine that is disconnected from the server.

Impact
You will never see that warning reminding you to update your Mac client connector.
If you don't have a Mac client, this alert will not show up anyway, so you can assume this alert is a false alarm.
No impact to other alerts or product features.

Workaround
1. Select any client computer in the “Computers and Backup” tab on the dashboard.
2. Check the “Operation System” value in the “General information about this computer” area on the bottom.
3. If the value is unknown, right click the client computer and select “Remove the computer”.
Note, If you see the clients are in the "Archived computer backups" category, please be aware that if you remove the computer, it will also remove all backups for that client.

“Computer Monitoring Error” shows on the Client after Server installed BPA.

This only applies to machine that installed WSSG 2011 BPA. You will find following Exception in the SharedServiceHost-ClientAlertServiceConfig.log file under %Programdata%\Microsoft\Windows Server\Logs on the client.

[2216] 120223.103228.7431: AlertFramework: Subcomponent: HealthEvaluator > Condition Evaluation for HealthDefinitionName=BPAChecker_Scan FeatureName=WSSGBPA threw an  exception: Microsoft.WindowsServerSolutions.NetworkHealth.Engine.ActionRuntimeException: You cannot call a method on a null-valued expression. ---> System.Management.Automation.RuntimeException: You cannot call a method on a null-valued expression.

Cause
It is caused by the BPA Alert evaluation component. This alert evaluation is designed for server only.
When it is running the client, it cannot find proper BPA files, and throw an exception instead exit silently.

Impact
You will see a “Computer Monitoring Error” on the client, there is no impact to BPA functionalities, as BPA will not run on client.
BPA alerts on Server, other alerts or production features are not impacted.

 

Workaround
1. Uninstall BPA on the server
2. Install BPA on the server again,  do NOT select the check box “Integrate Windows Server Solutions BPA scan results in the server console.” Be aware that you will not see  BPA scan results in the server console after this. You can still open BPA UI to see the result.