Out-File: output file path is not accepted - powershell

Question

Still learning and am having a hard time trying to output information to a file: the output file path is not accepted.
My location is PS Cert:\localmachine and here is the entire command:
$cert = Get-ChildItem -Path cert: -Recurse | where { $_.notafter -le (get-date).AddDays(75) -AND $_.notafter -gt (get-date)} | select notafter, issuer, thumbprint, subject | sort-object notafter
$cert | Out-File -FilePath \\ad.dcpds.cpms.osd.mil\WinAdm\Logs\Expiring_Certificates\$hostname.log
The error message I'm getting is:
Out-File : Cannot open file because the current provider (Microsoft.PowerShell.Security\Certificate) cannot open a file.

Answer 1

Based on the comments above, the issue comes from the fact that the current location is somewhere in the certificate provider (cert:).
One possible workaround/solution is to change the current location back to the file provider before writing the file.
$cert = Get-ChildItem -Path cert: -Recurse | where { $_.notafter -le (get-date).AddDays(75) -AND $_.notafter -gt (get-date)} | select notafter, issuer, thumbprint, subject | sort-object notafter
Set-location c:
$cert | out-file -FilePath \\ad.dcpds.cpms.osd.mil\WinAdm\Logs\Expiring_Certificates\$h‌​ostname.log
Second solution: use a path that explicitly includes the filesystem provider:
$cert | out-file -FilePath FileSystem::\\ad.dcpds.cpms.osd.mil\WinAdm\Logs\Expiring_Certificates\$h‌​ostname.log

Answer 2

To complement PoorKenny's effective solutions with background information:
If you use Out-File and the current location is on a drive of a provider OTHER than the filesystem provider:
only drive letter-based paths are recognized as filesystem paths; e.g.:
... | Out-File C:\temp\out.txt # OK, due to using filesystem drive C:
any other path requires prefix FileSystem::, notably including paths such as \path\to\... and even \\server\share\path\to\... (UNC paths); without the prefix, they're interpreted as relative to the current location, whatever its provider, which fails for any provider other than the filesystem provider.
... | Out-File \temp\out.txt # NOT recognized
... | Out-File \\server\share\temp\out.txt # NOT recognized
... | Out-File FileSystem::\temp\out.txt # OK, thanks to 'FileSystem::' prefix
Arguably, given that Out-File only ever creates files, it would make sense to ALWAYS interpret the -FilePath / -LiteralPath arguments as a filesystem path, irrespective of the provider of the current location.
However, the following, from an example that comes with the Out-File help, suggests that the behavior is by design (the (omitted) example invokes Out-File from a current location on the registry provider's drive).
Because Out-File is not supported by the Windows PowerShell Registry provider, you must specify either the file system drive name, such as c:, or the name of the provider followed by two colons, FileSystem::, in the value of the FilePath parameter.
"
If anyone knows whether there truly is a good reason not to always default to the filesystem provider's current location, do let us know.
(Can there be additional, alternative filesystem providers?).