The problem with bitcoin and Security Essentials is easily remedied, and Security Essentials has worked flawlessly for me. I don't feel a need to go looking for something to replace it. If you're going to run Windows (which I don't necessary condone ), you might as well use Microsoft's free virus protection offering. As far as I can tell, it's waaaaaaaaay better than Norton or McCrappy or any of the expensive stuff, and since it's made by Microsoft you know that it'll cause lots of problems - I mean - you know that once they've attached their name to it they're going to be careful not to make it too crappy - well - they're going to... I don't know where I was going with that. I just think that I'll stick with Microsoft Security Essentials for now. That's all. B)

Ironically and interestingly, I started a JavaScript chatbot project that I named Jimmy a while back. He's still a moron, but he is excellent at answering yes/no questions. Plus, I designed the code to be highly customizable and supremely inefficient.

This worked for me too! Thanks. 
Microsoft Security Essentials was locking up the bitcoin.exe process. The thread with the solution has several responses from other people running various editions of Windows. The problem may extend to other virus protection software. You just have to exclude the bitcoin.exe process from its scan, and it's probably healthy to add the block database files to the exclude list as well. Of course, this opens the excluded files up to infection, but it's a risk you'll have to take until another solution can be found.

Excellent tip. Just applied this fix to two very different computers, both running different versions of Windows 7 (64 bit). Looks to me like this is a universal issue (at least in the case of Microsoft Security Essentials virus protection).