I've had my settings just right for YT for ages now and a standard template in place - no problem (standard size for me is PAL Widescreen 960 x 540).
Here's what I consider OK (one of the last vids rendered before the problem began)

(Actual link is
- this shows my point better - without it showing at full screen)
So last weekend, I rendered another vid and this is what it came out like:

(Actual link is:
definately demonstrates it better - without going full screen)
I've checked that all the settings are the same as the first one, I've checked the camera settings are the same and they are on both. The properties of both are the same. I just can't understand what has changed and don't know what else to check. Could the project settings possibly make any difference to the final render?
I have so many vids to put up and can't bear them not showing at the correct size so any suggestions would be extremely welcome.
Here's what I consider OK (one of the last vids rendered before the problem began)

(Actual link is

So last weekend, I rendered another vid and this is what it came out like:

(Actual link is:

I've checked that all the settings are the same as the first one, I've checked the camera settings are the same and they are on both. The properties of both are the same. I just can't understand what has changed and don't know what else to check. Could the project settings possibly make any difference to the final render?
I have so many vids to put up and can't bear them not showing at the correct size so any suggestions would be extremely welcome.