I ran into the error, below, because the host instance didn't have permissions to read the C:\Program Files\Microsoft BizTalk ESB Toolkit 2.0\esb.config file. Also, don't forget to restart your host instance (or run iisreset) after you update your permissions.
Event Type: Error
Event Source: BizTalk ESB Toolkit 2.0
Event Category: None
Event ID: 6060
Date: 2/9/2010
Time: 2:03:58 PM
User: N/A
Computer: XXXXXXXXXXXXX
Description:
Error 194008: An error occurred reading the, esb, Section in the config file.
Source: Microsoft.Practices.ESB.Resolver.ResolverMgr
Method: System.Collections.Generic.Dictionary`2[System.String,System.String] Resolve(Microsoft.Practices.ESB.Resolver.ResolverInfo, Microsoft.BizTalk.Message.Interop.IBaseMessage, Microsoft.BizTalk.Component.Interop.IPipelineContext)
Error Source: Microsoft.Practices.ESB.Resolver
Error TargetSite: Microsoft.Practices.ESB.Configuration.ESBConfigurationSection get_ESBConfig()
Error StackTrace: at Microsoft.Practices.ESB.Resolver.ResolverConfigHelper.get_ESBConfig()
at Microsoft.Practices.ESB.Resolver.ResolverMgr.get_ResolverProviderCache()
at Microsoft.Practices.ESB.Resolver.ResolverMgr.GetResolver(ResolverInfo info)
at Microsoft.Practices.ESB.Resolver.ResolverMgr.Resolve(ResolverInfo info, IBaseMessage message, IPipelineContext pipelineContext)