This is a statement of Dave's official site,
It is with regret that I have been informed by my friends at C2 Ventures, Ben and Phillip, that I am not to be invited to C5 this year or any other Lucas Film associated events. After enquiring, the only thing I have been told is that I have "burnt too many bridges between Lucas Film and myself" - no other reason given.
I have also been advised by the promoter of Paris Manga in September that LFL have requested no photo opportunities with the 501 Squadron, even though I am commander in chief of the 501.
Sincere apologies to all my fans who were hoping to meet with me - I shall miss you too. As you will see from my events page I will be at many conventions all over the world so we can still keep in touch.
Apparently the story goes that he and Lucas have had somewhat of a feud for nearly 30 years now which started when Lucas accused Prowse of leaking some of the plot of "Return of the Jedi" to the press. Something which Prowse has always strongly denied doing.
Sorry if there's any Lucas lovers on here but I think it's terrible how he can do this, Prowse semi-retired from Acting years ago, he's had two hip replacements and has just beaten Cancer so his only income nowadays is through personal appearances and conventions which he loves doing.
Thats now been unfairly taken away from him, I've seen interviews with Prowse on television over the years and he's always come across as a Nice Man and a True Gentleman. To say he's been unfairly treated by Lucas Film is an under-statement, he still doesn't get his full share of the royalties from the franchise either.
Banning Darth Vader from a "Star Wars" Convention is like banning the Queen from attending the "Royal Variety Peformance".

I would love to hear your thoughts on this, I'm entirely on Prowse's side.