How to hide a block based on content type?
Sadly, it is not yet part of Context to negate the context (that I am aware of).

You have 2 options (slightly different than the link mentioned by @Mołot):


Write your own context.  It's actually not that hard, and you can follow the general flow suggested in (this post)[http://dtek.net/blog/extending-drupals-context-module-custom-condition-based-field-value].
Use the built-in visibility settings on the block configuration page to enable the block on all content types but the one you want, and all pages desireable (e.g, user/*, views pages, etc.).