mIRC is not a file trading program, it is not used for "downloading". The DCC Protocol was never designed to handle huge files that are over 1GB, nor was mIRC!
If the file you're downloading is a form of warez (i.e. movie) then you are breaking copyright laws which we do not help with on this forum. See
this post.
It is, I guess, possible that you're downloading something perfectly legal, but I'm sure you can imagine that I find that hard to believe when you mention 'XDCC', 'FServe', 'downloads' and '1.1GB' in the same paragraph! If you are downloading illegal files let me reiterate the point that we don't help with it here and do not encourage or condone it either.
Regards,