mIRC has nothing to do with G-lines on a network, you will need to contact the network administration for help with the issue. See this thread
for further information. It's helpful to both you and us if you would take the time to look at the sticky threads at the top of the forums, and/or to use the search feature before posting. This saves us from repeating information constantly.
As an added note, IRC is not meant for XDCC/mass file trading. Downloading mp3s, movies and so forth is illegal and makes you liable for heavy fines. Do not be surprised when programs such as XDCC Catcher get banned, or you get banned for using the program, because you are effectively abusing IRC by doing so.