Why does System.IO assembly give linker errors in Unity 3 when they worked fine b4

All script compilation fails whe dealing with System.IO assembly. Previous version of Unity were able to compile these assemblies without problems. Now, all I get are errors about how FileInfo, FileStream or functions like Create are not defined. Yet, try exist in the Mono Develop editor so much as to even give me the intellisense and definition of these strutted & functions.

I hope this is a temporary beta problem. Because if not, Unity 3 iPhone will be a useless upgrade since these capabilities are crucial to the function of our. Game's multiple profile system.

Unity has been segmenting out parts of the .Net API depending on your build target. System.IO is for instance no longer available at compile time if you're building a web player, but is for desktops. I haven't tested it on iPhone, but it seems from your post they have removed it from there as well.

Most probably you are working in Web Player mode. You can switch to iPhone mode by clicking File->Build Settings..., selecting "iPhone, iPod Touch and iPad" and clicking "Switch platform" button.