Newbie pythoner, with bizzare problem

[Jack]

Hey there, 

im pretty new to using python, and im just experimenting with file access, 
a wrote a script that works fine, and then all of a sudden it started 
throwing up this error:

inp = open("c:/autoexec.bat",'r')
TypeError: illegal argument type for built-in operation

it was working fine before, and i dont see anything unusual in the syntax.

Any help would be appreciated,

Cheers, 

Jack Green