Custom MIME Type

I have some simple asp code to send a response to the client with aparticular ContentType defined, code shown below:

Response.Clear
Response.ContentType = "application/x-custom"
Response.Write "<?xml version='1.0' encoding='UTF-8'?><testing/>"
Response.Flush

I have a client side ActiveX control implementing IPersistMoniker that isregistered to handle this MIME type. This seems to work fine on some machines and not others. On some of my machines, the control is not instantiated at all. Instead, a blank page is shown in the browser. If I change the ContentType above to something like "text/xml", the response is shown correctly in the browser. This leads me to believe there is a problem with the client mime handler, but it seems to work on most machines.