Since the hosts file is often used and altered by malware to hijack your computer, a lot of protection programs (some Antivirus, most Anti-spyware/malware/adware programs) block it from being opened by external apps so it cannot be changed without your knowledge. The most likely case here, is that Spybot is trying to check to see if your hosts file is clean and is being denied access to that file.
Here's some information for you on what the hosts file is and how it is used.The Hosts File and What It Can Do For You
If you don't have any symptoms of infection (pop-ups, unexpected redirects, hijacked search results) I wouldn't worry too much about it.
Additionally, if Spybot locked it (because it can), you can disable that feature by following the instructions posted on the Spybot forums here.
And uninstalling, reinstalling it won't change the end result.