If you run a process (such as Visual Studio) elevated (as you claim in comments), it's not running as your current Windows user, but as Administrator.
Administrator does not have the drive mappings that your user has. So your Visual Studio cannot see the P: drive at all, because that mapping is specific to your user.
See How to access network shares from an elevated process in Windows 7?: if this error is caused by your current user having the P: drive mapped to a network drive, you can use the UNC path to the share instead: \\server\share\file.xml, where P: would be mapped to \\server\share\.
