Greg,
With 2.6.17-rc6-git2, I'm seeing this kernel message during start-up:
pl2303 ttyUSB0: pl2303_open - failed submitting interrupt urb, error -28
The pl2303 serial port is part of a USB1.1 Hub/dock device,
plugged into a USB2 port on my notebook.
I get the same failure again when trying to use the port with Kermit.
This device was working fine here not long ago -- on the -rc5 kernels I think.
Unplugging the hub/dock does this:
kernel BUG at kernel/workqueue.c:110!
invalid opcode: 0000 [#1]
PREEMPT
...