What. You're probably here because an admin commented DWD.is/error on your post. That means that even though you can see your attachment, most people can't. Instead, they see "Attachment Unavailable." Here's what it looks like:
We want all members to see your posts, so please learn how to fix it right away. Don't worry. It's easy.
Why. The default privacy setting for personal pages is Friends Only. When you share a post you originally posted to your page (as opposed to posting directly), the Friends Only setting remains with the attachment. The result is that only you and your friends in the group can see what you are trying to share, while everyone else sees the Attachment Unavailable error message instead.
How to fix it. You don't have to delete your post. Assuming the original attachment is yours, just go back to your personal page and find the original attachment. Edit its Privacy setting and change it to Public. Your shared post will update automatically. If the attachment is not yours, then ask the owner to do the same. If you're unable to get ahold of the content owner, then please delete the shared post and post the content directly instead.
Tip. It's easy to quickly determine the the privacy setting of a post. Just look at the little icon at the top. A globe means Public. Two people means Friends Only. Two people in a box means posted to the Group.