[Mikuro]

You say that changing something to 'id' fixed it, so my guess is that you were referring to a class that had not yet been loaded by the compiler. Are you sure you have all the necessary #includes in that .h file?

I've run into similar-sounding problems before when I had two classes that cross-referenced each other. Since they relied on each other, neither could be compiled until the other was compiled. I've still never found a really good way around that, so I just change my types to id (or whatever the closest parent class is), and typecast in my .m file when necessary.