The cforms WordPress Plugin you’re using is not properly sanitizing input variables prior use, that’s why you get the warnings.
You can either fix the problem your own if you’re a coder, or report the issue to the plugin author and discuss if she can fix it.
But from what I googled, there is another version of that plugin, called cfomsII (WordPress Plugin). It will probably have this issue already fixed so perhaps changing the plugin to the new version is the best suggestion to give.