Need to pass in an output location on aspx page to a VB DLL to display text

I want to create a function in a vb dll that takes, as parameter, a location where data can be output to. Ultimately the plan is to be able to use the function in the dll to display messages for a windows app or a web app to an "output" location of choice (ie message box, etc) that the calling page/app would pass in.

Currently I am able to pass a label control from a web page to the function and the function is able to set the text value for the control but when control comes back to the calling aspx page, the text is not displayed on the label that was passed in.

Can anyone tell me if this can be done and if so what would I need to do to be able to see the text on the aspx page.