Matt, I tried that recently with one of my own sites, and after a few days I got a warning in my Google Webmaster Tools dashboard that the bot could not access my /search URL because it was blocked in my robots.txt, and I should take action to correct it. So I then unlocked my /search URL, which is in violation of the above guideline, but made the error in Google Webmaster Tools go away.
These conflicting messages from Google are very confusing!
In that case, Google Webmaster tools is not actually reporting an error. That's a report to show you what URLs Google tried to crawl but couldn't (due to being blocked) so you can review it and ensure that you are not accidentally blocking URLs that you want to have indexed.
I agree that it's confusing in that the report is in the "crawl errors" section.
(I built Google webmaster tools so this confusion is entirely my fault; but I don't work at Google anymore so sadly I can't fix this.)
These conflicting messages from Google are very confusing!