That is because the correct way to give the path in this case would be register.aspx?id=jSmith
, without the quotes. If you need spaces, or other special characters, in your ID, these should be URL encoded (and will be decoded by your code), but not enclosed in quotes.
For example, if your id was the string john smith
, the URL would become register.aspx?id=john+smith
, since +
is the URL encoding of a space.