Do you have permissions to traverse all dirs in the path from the source to G :/ perl / Alex Clare - The Lateness of the Hour / and write permission in that dir?
Is the space between the drivename, 'G,' and the colon (as shown in your report of the error message) an artifact of something here, or is it actually in your code? [update: I note that your post here on that point and your SO post are not the same. </update>]
Is your system one in which windoze balks at spaces in paths & filenames?
And re "modify the tags of the mp3 file," check CPAN for the plethora of modules with 'mp3' (or /mp3/i) in their names.