Not Able to Make Any Changes

What does this (below) mean?
Warning: fopen(d:\inetpub\sites\www.thatgrrl.ca\web\blog/wp-content/themes/default/header.php): failed to open stream: Permission denied in d:\inetpub\sites\www.thatgrrl.ca\web\blog\wp-admin\theme-editor.php on line 55

Warning: fwrite(): supplied argument is not a valid stream resource in d:\inetpub\sites\www.thatgrrl.ca\web\blog\wp-admin\theme-editor.php on line 56

Warning: fclose(): supplied argument is not a valid stream resource in d:\inetpub\sites\www.thatgrrl.ca\web\blog\wp-admin\theme-editor.php on line 57

Warning: Cannot modify header information – headers already sent by (output started at d:\inetpub\sites\www.thatgrrl.ca\web\blog\wp-admin\theme-editor.php:55) in d:\inetpub\sites\www.thatgrrl.ca\web\blog\wp-admin\theme-editor.php on line 58

I’m just so fed up. I can’t make even the slightest change to my theme without all this coming up when I try to save it. I only installed it yesterday. It seems to let me post just fine. But I’ve been looking at themes (most of which will not work cause they say there is no stylesheet). The odd time I do find a working theme I get all this jumble of code if I try to change anything, even just changing an image file.

Is this a problem with how I installed WP cause I really can’t see why it is such a frigging hassle to make a minor template/ theme change.