Copying and pasting links from a previously sent email with click tracking already appended can affect click tracking URLs in the next email send so that Outlook will not be able to open these lengthier URLs.
If your links are not opening when clicked in Outlook, try cloning your sent email and check that you have inserted the links into the email editor appropriately. Always link to the final destination URL of your page (i.e., http://offers.yoursite.com/yourpagetitle). There is not a way to fix these retroactively for emails already sent; however, the links can be copied and pasted from Outlook into a web browser.
If your email link is leading to an error page, check out this article.