I just did it in mine without any issues.

Are you receiving any errors?          Is there any particular reason why you would place this code inline with your presentaiton layer?

It would make more sense to use a Label and populate it with code-behind when an event takes place... ie page_load etc.

There shouldn't be much of a problem inserting the data into a TextBox.      What would the URL consist of?    Under what conditions is it generated?     It really sounds to me like you should be doing this in the code-behind for the form.

Here's an example...   The TextBox is placed in your form:

<asp:TextBox ID="mytextbox"></asp:TextBox>

And suppose you generate this url when a user clicks a button

Inside the button's event handler, you'd have code like this..

Dim url As String

url = ???  something that you need it to be...

mytextbox.text = url & UserController.GetCurrentUserInfo.Username

... or whatever.

I'm kinda shooting in the dark here, but that's what I would be working on.  If you ever have to change the way your code behaves, it will be much easier to edit if it's not spread all over the form with <% tags.