Thanks for your bug report and feeback.
An intermittent crashing issue with v7.62 was reported by some users. A fix was applied that resolved the issue for them. However, the issue you are seeing sounds very similar.
Which version of mIRC were you using before v7.63?
Did the issue with v7.63 begin immediately after using it?
If you restart your computer, do you still see the same issue?
