I get an error almost exactly like this everyonce and a while when i close. Mostly when mIRC has been running for several days (often 1-2 weeks)
Its not a router issue, as i have't had to do any router changes.. and i still get the error.
heres a screenshot of the error :
Its the same instruction causing the error > "0x7c91e9c9"
but different memory location.
So far it seems that it does no real harm to mirc.. no courpt ini files or chopped log files when the error orcures. It just happens.