Hey there,
There is no known exploit in mIRC 6.14 so it's not an exploit of some sort. In the unlikely event you're running SysReset script, unload it. If you're running a large amount of DCC sessions then try closing them.
I suggest you install a fresh copy of mIRC to a different directory and run that mIRC, with no scripts, for just a day or however many hours (at an estimate) it usually takes mIRC to crash. If it doesn't crash then it's probably a script. If it does crash then it might be a Windows issue.
If there anything specific you're doing before mIRC crashes? A command? A popup or anything?
You might wish to check for viruses, there are a few trojans out there that use that DLL, might be causing the issue. Some antivirus resources can be found
here. Make sure you actually have the DLL, usually in C:\WINDOWS\SYSTEM\MSVCRT.DLL for Windows XP. Don't touch it, just see that it's there! It probably is for such an error to occur.
That DLL is apparently part of C's runtime library, you can download it
here if you don't have it. You may also find
this article of interest. Also
this thread has some interesting thoughts.
Hope this helps
Regards,