Invalid Uri : The uri scheme is not valid

WebRequest req = WebRequest.Create(formUrl.Trim());

string url,string username,string password come from a text box. This is the full code:

public void LoginToUrl(string url,string username, string password )

 {    

 formUrl = url;    

 formParams = string.Format("username={0}&password={1}", username,password); 

WebRequest req = WebRequest.Create(formUrl.Trim());//  

req.ContentType = "application/x-www-form-urlencoded";    

 req.Method = "POST";      

 bytes = Encoding.ASCII.GetBytes(formParams);     

req.ContentLength = bytes.Length;     

using (Stream os = req.GetRequestStream()) 

{         

os.Write(bytes, 0, bytes.Length); }

 WebResponse resp = req.GetResponse();     

cookieHeader = resp.Headers["Set-cookie"]; 

}

This is the POST Data:
Host=internetlogin1.cu.edu.ng
User-Agent=Mozilla/5.0 (Windows NT 10.0; WOW64; rv:37.0) Gecko/20100101 Firefox/37.0
Accept=text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
Accept-Language=en-US,en;q=0.5
Accept-Encoding=gzip, deflate
Referer=https://internetlogin1.cu.edu.ng/login
Connection=keep-alive
Content-Type=application/x-www-form-urlencoded
Content-Length=49 POSTDATA=dst=&popup=true&username=13ck015373&password=F3NB