The filename in the RESUME CTCP is purely a placeholder. mIRC uses the IP and Port to figure out which DCC it is resuming, and ignores that parameter.
What is breaking your DCC resumes is your firewall/router software. It has a module loaded that intercepts DCC CTCPs and changes the IP/Port to that of the firewall, so that the person you are sending to connects to it instead of trying to connect to your inaccessable private IP. When the recipient requests a RESUME, the IP and Port included in the request are that of the firewall/router, not your local machine, so they don't match up with any of mIRC's pending transfers, causing the 'invalid parameters' rejection. Either disable this module/feature on your firewall/router and use static port forwarding, or update your firewall/router software with a version that corrects the RESUME bug.
