I don't know for sure but AutoComplete seems to get confused sometimes. For me it usually doesn't work if the source file I am editing does not compile properly (I guess it cannot parse it itself, which is fair enough, although rather frustating). I have heard that sometimes the database used by AutoComplete gets currupted. Try exiting DevStudio and deleting the NCB file, then recompiling. As I say I am not sure so this could be all wrong, but I hope it helps