[DotGNU]"is not declared in this scope"

[S11001001]

Ok, I made pnetlib, and most of the compiler errors go along these lines:

...is not declared in this scope

Now, just taking a small sample...

System.UriBuilder references System.Uri. However, I didn't put a using 
declaration at the top of the file, because after all, UriBuilder is in the 
same namespace. However, when there is a using declaration, as with 
System.Text, classes from those work.

Does a namespace have to be imported with a using declaration, even if the 
statement is inside the same namespace?

--
I've run DOOM more in the last few days than I have the last few
months.  I just love debugging ;-)
        -- Linus Torvalds