Help me fix a type of variable in program send a recieve fil

Question

Hi everybody, I have write a program send and recieve a large file , now it can transfer a file size 1.5G but when I choose  large file about 2G it fail and notify:
http://i1055.photobucket.com/albums/s505/vn_photo/Untitled-27_zpscf61b7a1.jpg

Here is Project:

http://www.mediafire.com/?p9b2xj2970d7cqb

Please read and help me, it code is short, no long, I need a help I'm nearing to send it for my teacher, I hope everyone will help me.