'document.body' is null or not an object (line 3044) (socket.io.js)

I have two copies of the same site, with the same source code, where this error shows up in IE7 on one of them. This is with socket.io 0.8.7 (and now.js 0.7.6).

The line in question is:

```
document.body.appendChild(form);
```

Obviously, this code runs too early due to some weird timing issue I can't figure out. Why could this happen?
