I changed line 28 in
PowerShell/SQLUtility/SQLUtility/Copy-SQLLogins.psm1
from
$filename = $source.Replace('/','_') + '_' + (Get-Date -Format 'yyyyMMddHHmm') + '_logins.sql'
to
$filename = $source.Replace('/','_').Replace('\', '_') + '_' + (Get-Date -Format 'yyyyMMddHHmm') + '_logins.sql'
I had a backslash error when using a named instance.