Custom Credential Provider Command Link to to open a browser with URL, does not open browser

Question

I have written a Custom Credential Provider (Wrapper) [in VC++] to show a command link, when clicked on it will open a browser with a URL. It works fine in my development environment. But after installing the DLL and completing the registering settings on a Client environment, it shows the Command link on the Windows logon screen. But when clicked on it no response. Only first time it invoked the Default Application Selection window to select the application to open and after selecting the browser, it didn't show anything, also, from the second time onward when the link is clicked it does not show anything.

The code is;
ShellExecute(0, 0, "URL name", 0, 0, SW_SHOW);

I want to know the following, plus additional information that I am NOT aware of, which you may provide.

1. How to catch the exception from ShellExecution, and what are the Exceptions?
2. The client environment has a Group Policy to enable / disable internet access to certain users, in which case, how should I enable internet access only during the Windows Logon session?
3. What are the properties in Windows that I should check for, in order enable the user to gain internet access (so that the browser will open), and open the browser with default URL. I understand that once the user have access to the browser he/she may browse through various sites, which we cannot control.
4. Am I missing anything on conceptual background about Windows Logon screen such as, the limitations (what are allowed to perform, and what are not / must not do), that I should learn first, and proceed further.

Thanks in advance for your help.

Regards,
Giri.