RenderPageToString, generates a empty image page

Hi, I need help with this problem.
When I generate an image of a page using RenderPageToString, only with some specific PDF files which were generated by scan or fax a printed document, the result image is a blank jpg with the page’s dimensions. The content of all these files is a scanned image set as page’s Background. Think the RenderPageToString method ignores the content of the background. Let me know if there is a way to configure the render to not ignore the background.

This is mi wrapper implementation:

public byte[] RenderPageToString(int DPI, int Page, int Options)

{

  if (this.dll == null)

  {

    return new byte[0];

  }

  IntPtr source = this.dll.QuickPDFRenderPageToString(this.instanceID, DPI, Page, Options);

  int length = this.dll.QuickPDFStringResultLength(this.instanceID);

  byte[] destination = new byte[length];

  Marshal.Copy(source, destination, 0, length);

  return destination;

}

I am using
C# in Visual Studio 2010
.Net Framework 4
QuickPDFDLL0718.dll