404 The Requested Page Cannot Be Found

I have created a sign-up form selecting the fields from the available options; the code is pasted below for reference. Then, when I go to preview the form, I get this error message (the short code also does not work when placing it elsewhere):
“404
THE REQUESTED PAGE CANNOT BE FOUND
Can’t find what you need? Take a moment and do a search below or start from our homepage.”

Any suggestions? Thanks!

Form Code:
<p>
<label>First Name</label>
<input type=”text” name=”FNAME” placeholder=”Enter your first name” required>
</p>
<p>
<label>Last Name</label>
<input type=”text” name=”LNAME” placeholder=”Enter your last name” required>
</p>
<p>
<label>Email Address</label>
<input type=”email” name=”EMAIL” placeholder=”Enter your email address” required>
</p>
<p>
<input type=”submit” value=”Sign Up”>
</p>