I am using Invoke-Sqlcmd from SQLPS to execute a stored proc, and want to output a log to a path on the remote server that I get earlier in my script.

So first I get the path by querying a table, and capture it in a $Path variable:
$Path=Invoke-Sqlcmd -Query "select value from MyTable where name = 'Path';" -Database MyDB -ServerInstance "$Servername"


I then try to execute my stored proc, and put the output to the path I got earlier:
Invoke-Sqlcmd -Query "EXEC MyStoredProc;" -QueryTimeout 65534 -Database MyDB -ServerInstance "$Servername" | Out-File -filepath "\\" + $Servername + $Path + "LogOutput.txt"

But I get an error:
Out-File : Cannot validate argument "+" because it does not belong to the set "unicode, utf7, utf8, utf32, ascii, bigendianunicode, default, oem".

So it doesn't look like I can do that, but I need to. Can someone help?

Simple!

Invoke-Sqlcmd -Query "EXEC MyStoredProc;" -QueryTimeout 65534 -Database MyDB -ServerInstance "$Servername" | Out-File -filepath $("\\" + $Servername + $Path + "LogOutput.txt")

isn't it?

You're missing "\" also here. Please take care of them.

Nope, I tried that. I build my path based on cancatination of instance name and previous variable $Path1 that I get initially in the same script, like so:

[string]$MyPath="\\" + $Servername + "\" + $Path1.value.Replace(":\","$\") + "DBBackup.txt"

But nothing gets logged. If I execute this stored procedure from a job I get a nice output file that looks like

Processed 440 pages for database 'MyDB'...etc

I load sql assembly like and create an object this
[System.Reflection.Assembly]::LoadWithPartialName('Microsoft.SqlServer.SMO') | out-null $SQLserver = New-Object ('Microsoft.SqlServer.Management.Smo.Server') $Servername

# Create Databases object
$dbs = $SQLserver.Databases

#Here I execute my stored proc

#then I want to iterate through dbs and log backup status for each database:

foreach ($db in $dbs) { Write-Debug "Backing up $db.Name on $Servername "
 if ($?) {"Successfully backed up " + $db.Name + " to " + $Path.value | Out-File -filepath $logFile -encoding oem}
else {"Failed to back up " + $db.Name + " to " + $serverBackup.File | Out-File -filepath $logFile -encoding oem} }

But the only this that gets logged is
Successfully backed up tempdb to C:\MyPathHere