Header.php Error

[Igal]

Hello everyone,

I'm quite new to php and even more to the WordPress, I started my first blog about 2 weeks ago and my first problem to which I wasn't able to find a solution by myself came even earlier than I thought.

I was waiting for my Logo that a friend of my designed specially for me and now that I have it, I'm stuck in the very first step of replacing the existing header.

What I did so far was to upload the new logo with the Winscp, then I logged in>Appearance>Editor>Header(header.php)

Since then, I can't make any changes, when I click on "Update file" (even if I don't change anything) I'm forwarded to a 404 page: "Not Found, Error 404

The page you are looking for no longer exists. Perhaps you can find what you are looking for by searching the site archives by page, month, or category:"

Any ideas what might cause it? As it's such a popular CMS I guess somehow I did something wrong..

I'll appreciate any help at the moment

Thanks a lot!