problems with one RangeLAN-DS(hostap) and clients using USB cards

[BartOwl]

hi everyone!

i have a Proxim RangeLAN-DS card using hostap (first the stable version,
but now also the CVS) and a very strange problem..
having 2 identical USB cards workin' in managed mode under WinME and
Win98se2, on different hosts i experienced, that on one of this hosts
everything works ok, transfer speeds of ~600 kb/s and no link
problems...
the other host has a strange problem - its signal level is either ~60%
or none (it looses association to the AP)... especially when fetching
big amount of data... the transfer speed also wasn't ever over 1.5Mbit,
and after a few minutes that host looses the link... i don't think it's
a problem of radio signal strength... could it be, that USB generates
too much CPU overhead and that host (which is an AMD-K62 300Mhz) just
cannot synchronize all that? that host which works clear is an Duron
800Mhz...
and now some logs from AP - it may help...

wlan0: STA 00:90:96:38:ad:f2 TX rate lowered to 55
wlan0: STA 00:90:96:38:ad:f2 TX rate lowered to 20
wlan0: STA 00:90:96:38:ad:f2 TX rate lowered to 10
wlan0: sending disassotiation info to STA 00:90:96:38:ad:f2(last=19072887, jiffies=19102987)
wlan0: sending deauthentication info to STA 00:90:96:38:ad:f2(last=19072887, jiffies=19103087)
wlan0: Could not find STA for this TX error

for me it seems like that station has just timeouted or smth... i'm
sitting at this problem a little of time and have no other ideas...
would appreciate any help.
-- 
BartOwl <bartowl at surufje.w.pl>