Hi All, I am facing some issues while running LoadGen in my environment. I have described my scenario below: We have a lab setup where there are several Exchange versions installed. (2003 and 2007). Now when I try to run LoadGen (within the domain with exchange management tools), it tries to identify the complete topology. It does identify all the Mailboxes present in the environment but it shows all the mailboxes as grayed out. When I looked at the logs, it shows me below error. RecipientBuilder Warning: 0 : 3/30/2010 4:59:23 PM -- The target topology will be marked as not editable because there are users created by either other tools or previous version of LoadGen, e.g. Ls5jwdvaaa. And rightly pointed out, i have many users that were created by LoadSim. So I deleted all the users that were created by LoadSim from all the Mailbox Databases. Now when I run LoadGen again, the topology is still grayed out with the below error. RecipientBuilder Error: 0 : 3/31/2010 4:04:54 PM -- Unable to read serialNumber of server W2KEXCH2K3:System.ArgumentOutOfRangeException: Length cannot be less than zero. Parameter name: length at System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy) at Microsoft.Exchange.Swordfish.Extensions.RecipientBuilder.Topology.FindDirectoryObject(String[] attributesToLoad, DirectoryObjectBase parent, TopologyObjectType objectType, Topology topology, String filter, String dc, String baseDn, String directoryUsername, String directoryPassword) The machine (W2KEXCH2K3) shown in the error is up and running well. Actually there are several machines for which it gives the same errors in the logs. Have anybody faced such kind of an error ? Is there any way I can bypass the topology scan and enter the configuration details manually ? Thanks, Aakash