PySerial and termios

[a b]

I have a pain in the a** problem with pyserial- it works 90% of time
but on the 10% of time it thorows and termios.error exception with the
value (5, 'Input/output error') and i cannot get rid of it :(
The system works as follows:
A device sends out rs485 data -> rs485 to rs232 converter converts it -
> an rs232->usb cable attatched to a computer reads the data. Until
now it hasn't bothered me too much since it hasn't been a lot of data
(every time i get this exception i unload the pl2303 module from
kernel, then reload it, open the com port and hope it won't happen
soon). But now the amount of data is getting bigger and the exceptions
in the log are quite bothering already so if anyone has a good idea
what could affect it i'd be very glad...
oh and the settings for the port opening are:
self.ser = serial.Serial(self.port, self.baudrate, rtscts=0,
xonxoff=0, timeout=0)

With best regards,
Tanel