We're all on different ISPs and even in different countries - I use British Telecom, another friend uses Wanadoo in France and another is on a US ISP - not sure which one. Common problem: none of us could DCC send under 6.1x, but we could once we went back to 6.03.
And we don't use scripts - we basically just hang out on an IRC channel and chat. About all we do other than that is play the occasional wav - all of which work fine - and use stuff in the .ini file (the slap, op, kick commands etc). When we DCC, it's almost always sending Word files to each other - we write fanfiction.
So... <shrug> can't think of anything which gets in the way.
Thanks for trying to help, though.