Pyserial not working upon reboot

[Basheer]

Hi , 

I've got a python script talking to one of the serial port via pyserial. It works fine when I execute using the terminal. If I place it under startup, the behaviour is changed. It doesn't work properly compared former. Has anyone come across this problem. Advise/help is appreciated.  

[martinayotte]

I don't see why behaviour is different.

Provide more details, show the script, and how did you place it in startup (/etc/rc.local ?)