The Libraries location is not available to users. If you want to save your files, you must select a location on Computer, whether it is on the hard drive ("Desktop" for example) or something attached such as an USB drive. The below interface is identical for both PCs and Macs ("C:" is the Local Disk on Windows and "H:" is the user space on Macintosh).
Remember Documents library (and anything under it) is not available. Avoid saving in Documents library. Save As gives you the following:
SelectComputer, then select a preferable location (such as a USB device), and clickSave (Shown is a Windows 7 example).
ORSelectComputer, then select a preferable location (such as Desktop), and clickSave. Desktop is the same folder on both Windows 7 and Mac OS Users → your-user-name → Desktop.
Windows 7 Procedure
You may have a security warning. ClickPermit all access.
On Macintosh the H: drive is already Users → your-user-name. The C: drive is the operating system and applicatiations; it is not generally a writable location. SelectH:.
You may have a security warning. ClickRead & Write.