window.open resulting in "Invalid argument" error in IE

I kept getting an Invalid Argument error in IE while trying to execute window.open() in JavaScript.
Appearantly in IE you cannot use spaces in the name you give to the window.

So...

window.open("mypage.html", "my window name");

...does not work, while...

window.open("mypage.html", "mywindowname");

...works fine.

/Ruud