Method invocation failed because [System.Management.Automation.PSObject] doesn’t contain a method named ‘op_Addition’.

Sometimes you can get the following PowerShell error:

Method invocation failed because [System.Management.Automation.PSObject] doesn’t contain a method named ‘op_Addition’. 

Example:

$Update = $Searcher.QueryHistory(0, $historyCount) | Select-Object Title,Date
foreach ($update in $updates)
{  
    $obj | Add-member -Name "Server" -Membertype "Noteproperty" -Value $Server
    $obj | Add-member -Name "Installation Date" -Membertype "Noteproperty" -Value $Update.Date[0]
    $Results += $obj
}

$Results need to be a collection of $obj objects, not another object identical to $obj. So If you want to add PSObjects to a PSObject as a collection, use the following code:

$Results = @()
$Update = $Searcher.QueryHistory(0, $historyCount) | Select-Object Title,Date
foreach ($update in $updates)
{  
    $obj | Add-member -Name "Server" -Membertype "Noteproperty" -Value $Server
    $obj | Add-member -Name "Installation Date" -Membertype "Noteproperty" -Value $Update.Date[0]
    $Results += $obj
}

 

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