Thanks for your bug report. Please type the following command into mIRC and post your results:

Code
//echo -a $os $version $beta $md5($mircexe,2) $file($mircexe).sig $alias(0) $script(0) $dll(0) $com(0)

In order to help track down this issue, please also try the following:

1) Install mIRC 7.77 into a clean, empty folder using the portable option in the installer, with no scripts or DLLs.
2) Run mIRC, connect to servers, join channels, and so on.

Do you see the same issue with the clean install of mIRC if you leave it running?

If you do not, is it possible that one of your scripts is causing the issue? You will need to try to narrow down the cause of the issue so that we can try to reproduce it.

Also, if you type "/debug on" command in the status window, this will output debugging information to a debug.log file. This may help narrow down the cause if the crash is due to a particular server event.