Microsoft Operations Manager Event ID: 21185

How to resolve error 21185 :

For the update to work correctly, the local Network Service account must have full control of the HKLM\Software\Microsoft\.NetFramework\Policy\AppPatch\v2.0.50727.00000 registry subkey. To do this, follow these steps:

1. Grant the local Network Service account full control of the following registry subkey:
   HKLM\Software\Microsoft\.NetFramework\Policy\AppPatch\v2.0.50727.00000
2. Restart the MOM service on the management servers that have this update installed.

Download :
http://www.microsoft.com/downloads/details.aspx?FamilyId=F53F1EF3-A7A0-4C45-AEFC-7C1EC5DCCAA6&displaylang=en

QUICK NOTE: It could also been related to the time that MOM try to find computer. MOM check the Active Directory for the computer list and try to contact those computers. If those computers are closed at night that could be the reason why you still get this error message.