Problem With Trusted Connection (asp.net)

I am getting the following error when trying to access a database with
a trusted connection:

"Login failed for user '(null)'. Reason: Not associated with a trusted
SQL Server connection."

My connection string is:

"Server=MyServer; Database=MyCatalog; Trusted_Connection=True;"

Note that Anonymous Access is off in IIS, and I am able to read my
Windows login with:

Textbox1.text =
System.Web.HttpContext.Current.User.Identity.Name. Substring(System.Web.HttpContext.Current.User.Iden tity.Name.IndexOf("")
+ 1).ToLower()

Can anyone explain how to query the db using a trusted connection?

PS Is there a way to dynamically retrieve a list of databases the
current user has SQL rights on, by specifying only the server, again
using trusted connection?

Thanks...