Actually i found that its 32768 per file, and also from memory only on -l# (well as far as i tested which wasnt far smile )

Other writes function fine, so i still felt it might be some internal counter, but cant for the life of me think what the counter would be being used for, so maybe you are write its external to mirc, that the counters maintained in maybe the compiler (C is it?) has some internal routine values that ones overflowing, styill i cant think of what it would need it for.