Did you actually look at the capture? :D 

You have a ton of these:

So, this has nothing to do with a Diversion Header, it has to do with the fact that you have a '#' in your To Header, which is a no-no. Whoever is sending this invite needs to URL-encode it or remove the # sign. The offending header is this:

Brian West is wondering if this is from a Nextone device? Just curious. Anyway, have them fix the To header and you should be okay. (Note: the Diversion header also needs to have the # URL endcoded.)

-MC

P.S. - If they get their knickers in a twist over the URL encoding then throw the RFC at them:

Specifically, page 2 under "Unsafe:" you have this sentence:

The character "#" is unsafe and should always be encoded because it is used in World Wide Web and in other systems to delimit a URL from a fragment/anchor identifier that might follow it.