i had something similar to me happen in the past. the reason for it was a slow response from the identd server. you're likely connecting to a server that either requires an identd response, or has like a 3 or so second timeout on the identd response. the culprit could be either the identd in mirc itself, some other identd taking over mirc's, or you might not have the port forwarded or something like that.
those would be my guesses anyway.
