SQL2008SP3 Enterprise Edition: Getting an exception when trying to set an execution account

Hi Experts,

We have an SSRS installation on a box that has been running with an execution account for the last year or so. But recently when I tried to change the password for the execution account, I started getting an error like so:

System.Runtime.InteropServices.COMException (0x8004023F)
   at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
   at System.Management.ManagementObject.InvokeMethod(String methodName, ManagementBaseObject inParameters, InvokeMethodOptions options)
   at Microsoft.ReportingServices.WmiProvider.RSWmiAdmin.SetUnattendedExecutionAccount(String userName, String password)
   at ReportServicesConfigUI.WMIProvider.RSReportServerAdmin.SetUnattendedExecutionAccount(String userName, String password)

Could someone explain why this started happening suddenly? Let me know if you need any additional information from my side.

We are running SQL2008SP3 x64 Enterprise Edition.

Thanks,
Shahnaz.