The following error occurs when entering username and password information into the ArcGIS .NET ADF impersonation control.
Identity Validation Error: "Invalid username or password : The impersonation cannot be set. Refer to the ESRI Knowledge Base for more details"
The administrator who installed Visual Studio .Net did not add the developer's account to the 'VS Developers' group on the Operating System. Without inclusion in this group, the developer cannot populate the impersonation control attributes.
This error can occur even if the developer is a member of the Administrators group on the machine.
Log off and log back on to the machine in order for the changes to take effect.