Why did Gary Chalk stop illustrating the Lone Wolf books?

[Rune Owl]

I read somewhere that Joe Dever said Brian Williams was the natural person to replace Gary Chalk after Chalk stopped illustrating the books.  I'm curious to know why Chalk stopped doing it.  Does anyone here know?

[rhygar]

There was some sort of disagreement according to what I've read in interviews with Joe Dever. Check them out if you can find them. [edit: interview page 55/110 from 'Lone Wolf Miscellaneous'] 
Gary Chalk is on Twitter, you might try asking him openly on there? Let us know what the answer is if he replies.

[Rune Owl]

Thanks, rhygar. I'll read the interview you cited.

I did some reading about Gary Chalk a few weeks back because I was studying his art style from the early books. I sent him email to ask if he would answer a few questions about his process. So far he hasn't replied. If he does, I don't think I'll ask him about the disagreement.