I just spoke to Lacerte Customer Support about this. The representative I spoke with confirmed that on a NAS environment that I described the software is designed to give the read only warning. The fact that it is not is a problem. The rep thinks that it will still act as read only and when the second tax preparer tries to make changes to such a file, it will either give him a warning then or crash the software. I am going to test it and then get back to customer support to see how to proceed.