are you launching mIRC at windows startup? if so it could be getting executed before explorer.exe loads, and when that happens the taskbar can fail to display icons of running programs in the tray. that's not a problem with mIRC, but a problem of explorer not checking for any icons it should be displaying when it is launched, or perhaps there is no way for it to do this. if explorer.exe is crashing and being started again, it will also fail to display icons. try turning on the icon animation, as whenever icons that are not being displayed in the tray change, they tend to get displayed.