Where is the file? On your own hard disk, or on a network disk?
Are you able to save a new file to the same folder?
Oh, and is the actual error message longer - what is it exactly? And what system and Acrobat version?
It is not just a single file has this problem, but all. For this particular file, I have stored the file in my local D:/ drive and I am able to read and write in the same folder. I have Acrobat XI Pro with WIN 8 as OS. I have also Adobe reader 10.0.0 installed on my computer if this helps. The error message is as follows, when I click the OK button, it goes directly to a popup screen and advised me to change the file name.
Ok, you only gave us half the message. The chances are that the file is open. Most likely the system has the file open to generate a preview. Turn off previews in Explorer/Save dialogs.