My guess is that the file size is too big. Outlook.com's SMTP server automatically rejects attachments bigger than 10Mb. (To check on the file size, right-click on its icon and select 'Properties).
If so, you'll either have to upload the file to a hosting site (and then send the intended recipient a link to it) or, far simpler, use an email account that doesn't place a limit on the size of attachments. GMX (which I use) is about a zillion times better than Outlook.com and has no limit on the size of attachments. (You could either create a new account just for this one task or, better, use it as your main email address and then have all of your Outlook.com mail forwarded to it using the 'mail collector' facility):
http://www.gmx.co.uk/