Ran across a rather puzzling situation involving server (64-bit) hosting files for a 16-bit application. The customer is using Windows XP Professional for the workstations, which are connecting to a shared folder on the server (mapped to a drive letter). If the shared folder resides on a Windows 2003 server (32-bit) the application will launch on the workstation as expected. However if the same directory contents were set up on a Windows 2008 server (64-bit) -- the application will refuse to launch -- indicating that 16-bit applications are not supported (transferring the directory contents to local directory on workstation will allow app to launch). As far as I can tell they haven't set up Terminal Services.
update: I've been seeing a few references indicating that in 64-bit editions of Windows, DOS-style 8.3 short filenames are disabled by default. However, if that was the case, shouldn't the error message be different? (of course one could argue that the only applications that really required the 8.3 filenames were 16-bit apps -- hence the message could be considered accurate, though not particularly helpful in diagnosing the problem)...