The problem could be in several areas. Try reading
this thread Im sure there is either a manual or website for help with setting your firewall, we could only in general tell you it has to allow the ports you have set in options for mIRC to use to dcc send. (options/dcc/options)
If by invision, you mean the script, you will need to ask whoever wrote that for help. Several ppl have complained of problems with it. To test to see if thats the prob, get a clean copy of mIRC from
www.mirc.com, put it in its own directory (dont save settings) and see if you have any problem with dcc sends.
