Make sure you try using the Search feature, it may have been answered before (highly likely). Make sure you expand to 'All Forums' and 'All Posts' for best results. Common connection issues and an explanation can be found in
this thread. If you're experiencing 'Software caused connection abort', which is one of the most common errors to receive, then check out
this thread.
If you find you are 'G-lined' or 'K-lined' or 'AutoKilled', it means you are banned from that particular network and it has nothing to do with mIRC. See
this thread.
