It's not easy searching for the meaning of error codes, especially negative ones. The best I could find on this was some type of resource error.
-1712 is apparently a "timeout" error, meaning that some program tried to do something, and it couldn't complete the task and so it "timed out". This would likely occur if you are trying to access some external resource that isn't available.
I suggest trying several things in this order.
Quit & restart Pages
Use Disk Utility to repair permissions
Restart your Mac
As Peggy notes, a -1712 error is a timeout error for Apple Events. Often your Mac sends an Apple Event to a program asking it to start (when you double click an icon in the Finder) or to open a document (when you double click a document icon in the Finder).
Can you explain to us what action you're trying that causes this timeout error? And as Peter requests, please tell us the version of Pages you're using.
Open Activity Monitor located in /Applications/Utiliites
Select 'View' then 'My Processes' in the menubar across the very top of your screen.
Type Pages in the search field top right corner of the Activity Monitor window.
Now select the application Pages (it should say 'not responding') and click the force quit button that looks like a stop sign with an x in it.
>You should now be able to relaunch Pages.
Force Quitting within Activity Monitor is a quick and efficient way to handle most Applications "Not Responding" or seeming not to open with error -1712.
Just be aware that you may lose any unsaved work by force quitting an application.