I think this is an area that could use a small makeover. The "check" for a valid filename seems to happen way after the encode is launched. Sometimes I launch an encode with an invalid filename (some non-allowed character in there) but it will only cancel the encode after 10 long minutes of encoding depending on what I'm cooking. Which can be a bit of a pain.
So why not have the "check" for a wrong filename happen first and foremmost when launching an encode and telling you right off the bat what's wrong with your filename / what characters were not allowed ?
That's something that could save a lot of time and minimize mistakes, I think.

So options I was thinking about were the following:
1- Make the check happen -before- starting the encode and stop if filename is invalid
and/or
1- Improve the auto-naming of encodes (it usualy lefts off characters that are actually allowed)
2- Make a tooltip or something appear, that tells you what characters were not allowed in your filename