 <p><code>out</code> has two forms, <code>out &lt;imm8&gt;, al/ax/eax</code> and <code>out dx, al/ax/eax</code>. Your instruction matches neither of these, so it is malformed.</p> <p>Change your code such that the value you want is in <code>eax</code> instead of <code>ecx</code> (which might be as easy as <code>mov eax, ecx</code>) and use the second form.</p> <p>Assembler messages are often inadequate, so get your hands on an instruction reference.</p>