Are you opening a file from a file server? It sounds like you connection with the server was broken, or there is a problem with the server configuration.
When happens if you reboot, reopen InDesign, and open a file on your local hard drive?
Yes we keep all of our ads and everything on our server and work from our desktop pulling the ads from the server. But the server never actually disconnects. I placed my ad on my desktop and restored my computer. I haven't had an issue yet since i have tried this.