The FrontPage 2000 Server Extensions store the contents of the _vti_bin folder (traditionally stored in the content area) in the following path:
<Drive>:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\40\isapi
This folder is mapped into each site as a virtual directory. If this location is on a FAT partition, FrontPage considers it to be insecure. This is because you cannot set file-level permissions on a FAT partition. When installed on NTFS, the ACLs are set with everyone having Read and Execute permissions on this folder and its contents. This is in order to disallow the possible security threat of uploading malicious code to the _vti_bin folder and executing it.