I just installed the dotnetinvoice software and was able to make configurations changes without any problems. Next I *was* going to add a test client to my newly installed dotnetinvoice. Here is the result - an alert message as shown below.
"Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occured while processing the request on the server. The status code returned from the server was : 500"
*I think* I figured out the issue. It's because the email address is already in the system - as the admin contact.
Here's a screen cap:
http://f.imagehost.org/0318/dotneterror.jpg