If you have a UI and you mean to say the UI is hanging then implement your reading code in a different thread. Search CodePr.. for threading etc .... Caveat Emptor.

If you use the XML libraries in C# does it not work for your large file? I've never tried anything with a file that big. ɹǝʌo ɹoʇıuoɯ ɹnoʎ dılɟ sıɥʇ pɐǝɹ ʇ,uɐɔ noʎ ɟı