FDF Toolkit and security warnings

We create simple, personalized PDFs on our website by injecting a couple of fields using the FDF toolkit. However as our users have been updating their Acrobat, the PDFs no longer pop up and instead the user sees a yellow bar with this message: "Data from this site is blocked to avoid potential security risks". They don't know what to do with the yellow bar and calls are starting to overwhelm our customer support.

This is really basic stuff we're doing. Nothing elaborate or cross-domain. How can I keep my users from seeing this error?

Here is the ASP code:

// Create the FDFToolkit object
var FdfAcX = Server.CreateObject("FdfApp.FdfApp");
var outputFDF = FdfAcX.FDFCreate();

// Set the PDF doc to be loaded
outputFDF.FDFSetFile("http://" + Request.ServerVariables("HTTP_HOST") + "/" + pdfFile);

// Define and populate the FDF field variables be loaded into the PDF
outputFDF.FDFSetValue("MyField", mydata, false);

// Send out the FDF content
Response.ContentType = "application/vnd.fdf";
Response.AddHeader("Content-Disposition", "inline; filename=" + pdfFile.replace(/pdf/g, "fdf"));
Response.BinaryWrite(outputFDF.FDFSaveToBuf());
outputFDF.FDFClose();
Response.End();