I think fcs stands for Frame Control Sequence, this is just a check that the ppp packet is received correctly.
fcs problems are normally caused by a faulty connection.
Although I have heard about problems with some later versions of com.sys.
Are you using the same modem commands in windows and os/2?
You could try the injoy dialer www.fx.dk/dialer it performs better than the ibm doip dialer.
Maybe you could try turning off your firewall temporarily to see if it helps.