How do I get a success response from submitting a fillable PDF

I have a fillable PDF with a submit button on it, it submits the PDF using the javascript for the Fillable PDF submit button as:

var myURL=encodeURI("https://xxxxxxx.com/SubmitForm.php");
this.submitForm({cURL: myURL, cSubmitAs: "PDF"});

If all goes well, the server sends back an bare FDF just to say success:

/FDF
<<
/JavaScript << /After (app.alert("Submitted. Thank you.");) >>
>>
>>
endobj
trailer
<<
/Root 1 0 R
>>
%%EOF   
EOD;

It submits the whole PDF to my server and that part is great and works fine. The problem is that after its done submitting I get this error:

“Some features have been disabled to avoid potential security risks….”

What am I doing wrong? Like I said, its actually working fine, but still gives me this ambiguous error which leads my users to believe something is wrong & didn’t submit.

Does anybody have any idea what I could do to fix this? Is there a better FDF string I can send back?

Thanks for any help.