When you try to move an attachment from a page to a new one that haves a colon ( : ) in the title, Confluence will not allow you to do it with the following message:

The expected behaviour should be to only move the attachment without messages.

Steps to Reproduce

1. Create a page with Colon in the title (e.g. A Page with Colon: Testing)
2. Create other page in the same space
3. Insert a new attachment to the page (Edit > Insert > Attachment)
   
4. Once you do this, click on Save
5. Access the attachments information (Tools > Attachments)
   
6. Select the properties option in the right side of the attachment
   !properties.png*
7. Insert the page with colon name in the Page field
   
8. Hit the Save button and the message will be displayed

Workaround

Simply just remove the colon from the title of the page.