WordPress doesn’t seem to correctly map POST data

here’s my problem :

I have a .php file within my wordpress that do the following thing :

• with a form asks a NAME and to the user
• posts the data to this same page (action=””)
• if NAME is not empty, then do something, else ask for the NAME again

Here’s the code :

function loginForm(){
echo'
<div id="loginform">
<form action="" method="post">
    <p>Please enter your name to continue:</p>
    <label for="name">Name:</label>
    <input type="text" name="name" id="name" />
    <input type="submit" name="enter" id="enter" value="Enter" />
</form>
</div>
';
}


if(isset($_POST['enter'])){
if(isset($_POST['name']) && $_POST['name'] != ""){
   //do smth
}
else{
        echo '<span class="error">Please type in a name</span>';
    }
}

But here’s the problem : when i click without entering any name, then it’s fine, it works as expected : it returns the same page with an error message. HOWEVER, if I enter any name, it returns me “Page Not Found”, and the POST request fails (404)

What could be happening so such a thing happens ?

PS : excuse me for my probably bad english