This article is from the Programming VCOMM FAQ, by firstname.lastname@example.org (Taed Nelson) with numerous contributions by others.
A few people have seen the Zmodem protocol fail with errors such as "bad
packet format" on the receiving side. Other protocols seem to work just fine.
While this has been seen mostly with our own VCOMM ports, one person said that
they saw it on a high-speed modem with compression on.
The current theory is that this has something to do with high-speed data
transmission, but Hilgraeve has not responded.
The 28800 Modem FAQ (http://web.aimnet.com/~jnavas/modem/faq.html) suggests
that it may be caused by overrun errors.
There is also some data that implies that the problem is actually caused by
running the DDK Windows 95 debug kernel.