As I mentioned, it's not an outlined circle, it's a filled circle. But I already solved the problem and I think you guys from redgate should take note to alert users for common "Oh my god you're stupid" problems.
The problem was that Visual Studio crashed while I was out for a few minutes, then when I restarted it I noticed that all the assemblies were browsable and were decompiled. The problem is that, whe VS crashed, a few items got unchecked from "Choose assemblies to debug..." and a few were not, so I got some random behaviour and forgot to check the items checked there and I wrongly assumed that if I could browse the libraries, they were available for debug.
Thanks for the help.