Substitua as quebras de linha por espaços antes de usar $ Description.
$web = get-spweb $siteUrl
$caseLib = $web.lists | where {$_.title -eq $listTitle}
$query=new-object Microsoft.SharePoint.SPQuery
$query.ViewFields = "<FieldRef Name='LinkFilename'/><FieldRef Name='DocumentSetDescription'/>"
$query.RowLimit=500000
Write-Output "Header}Description" | Out-File "temp.csv"
do
{
$caseLibItems=$caseLib.GetItems($query)
$query.ListItemCollectionPosition=$caseLibItems.ListItemCollectionPosition
$listItemsTotal = $caseLibItems.Count
$x = 0
for($x=0;$x -lt $listItemsTotal; $x++)
{
$Description = $caseLibItems[$x]["DocumentSetDescription"]
$str = ""
if('$Description' -ne $null)
{
### Insert the line below to remove line breaks ###############
$Description = $Description -replace "'n"," " -replace "'r"," "
###############################################################
$str = $caseLibItems[$x]["LinkFilename"].ToString() + '}' + $Description
}
else
{
$str = $caseLibItems[$x]["LinkFilename"].ToString()
}
Write-Output $str | Out-File -Append "temp.csv"
}
} while ($query.ListItemCollectionPosition -ne $null)
import-csv temp.csv -delimiter "}" | export-csv -NoTypeInformation -Path "result.csv"
Write-Host "Exiting"
Resposta compartilhada por Piero.