Most DLLs probably need to be updated in one way or another for mIRC 7.1. There may only be a small thing that doesn't work, or there may be many things that don't. It all depends on what the DLL does. It could also be that you've only seen one thing because you're not using the DLL for other things that may not work.
When it comes down to it, if you can't reproduce it without any scripts or DLLs installed, then the DLL or script probably needs updated to work properly.
