Barcodes not scanning - printed using vb code, scanning using vb6 code

downloaded IDAUTOMATION39HC font from net and
copied to my systems' windows/fonts folder (Using XP SP2)

I printed barcodes from my vb6 program on labels ( corresposning to alphanumeric codes,
ex: JN235, MN620 etc)

printing correctly
but when scanned some bars are not scanned (ex: MN620 or none in the range MN621,
MN 622 ETC)

SOME BARS has NO PROBLEM READING CORRECTLY
I used font size 10
tried using 11 and 12 same result

WHAT WENT WRONG