If you are facing with the following problem when accessing the ECP:
Request for URL 'https://localhost/ecp/default.aspx?rfr=owa' failed with the following error:
System.TypeInitializationException: The type initializer for 'Microsoft.Exchange.Configuration.TenantMonitoring.TenantMonitor' threw an exception. ---> System.FormatException: Input string was not in a correct format.
On Event Viewer you can find this error:
MSExchange Control Panel - EventID 4
You can fix this problem going to C:\Windows\System32 and running lodctr /r, after the command finishes run iisreset /noforce.
Ussually this issue occours after update the Exchange 2010 to SP1.