Nunit Asp.Net - control name contains underscore problem

[Guest]

I can get Nunit Asp.Net to work fine with
standard textboxes and buttons.

However when the rendered HTML contains controls that
are named something like
<input name="_ctl0:tbUserName" ...

because the control is embedded within a user control or suchlike
then Nunit Asp.Net says it cant find the control
and throws an ElementNotVisibleException.

The underscore _ is causing me a problem

does anybody know how to get this to work?

Thanks
Charlie