Authentication problem with using advapi32.dll

[caldera]

hi,
I want to forms authentication with windows password. So that I import
advapi32.dll. Import code like this[DllImport ("advapi32.dll")]
public static extern bool LogonUser(String lpszUsername,String
lpszDomain,String lpszPassword,int dwLogonType,int dwLogonProvider,out int
phToken);

then using forms value
int token1;

bool loggedOn=LogonUser(username.Text,domainname,passwo rd.Text,2,0,out
token1);

This code is work in my Windows2003 server computer. But this code should
run in a web server which has Windows 2000. This code doesn't work properly.
Error message is "Invalid token; it cannot be duplicated" What is the
problem for this code. and how can I solve this problem.
Thanks for helps.