Windows 7 (64-bit) and the latest version of mIRC (7.19). I have to say that since I started working on this (from before I created this thread here -- literally a year ago) I used several versions of Windows, mIRC, and different compilers, all to no avail. Tried this with Windows XP, Windows Vista, and Windows 7 (32-bit and 64-bit). As far as compilers are concerned I used Visual Studio, Bloodshed Dev-C++ (which relies on MinGW I believe, and which is what I'm currently using), and even Cygwin. I've tried literally tens of examples/tutorials and setting variations (with unicode, without unicode, different frameworks and build options for each compiler (e.g. standard Win32 DLL, MFC DLL, etc), etc). I never once got it to work. Would you mind uploading your DLL somewhere so I can test it with my mIRC? If it causes the same problem then it must be my environment (although, like I said before, I've tried this on several different setups, i.e. different software settings but also different physical computers, e.g. my laptop, my desktop, from within a virtual machine, etc).