get-eventlog

I'm trying to read the last 7 days of relevant Security log entries on one of my DCs and I'm getting the following error. Is there a way to accommodate all the data that's being returned? I don't explicitly declare $eventlog as a particular variable type.

Clear-Variable -name eventlog
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (eventlog:String) [Clear-Variable], ItemNotFoundException
    + FullyQualifiedErrorId : VariableNotFound,Microsoft.PowerShell.Commands.ClearVariableCommand
 
Get-EventLog : Log "Security" could not be read to completion due to the following error. This may have occurred because the log was cleared while still being read. Index 81445 is out of
bounds.
At D:\tsg\Documentation\Powershell Repository\adaudit.ps1:163 char:13
+ $eventlog = Get-EventLog -LogName ‘Security’ -ComputerName $domaincontroller -In ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ReadError: (:) [Get-EventLog], ArgumentException
    + FullyQualifiedErrorId : LogReadError,Microsoft.PowerShell.Commands.GetEventLogCommand
Get-EventLog : No matches found
At D:\tsg\Documentation\Powershell Repository\adaudit.ps1:163 char:13
+ $eventlog = Get-EventLog -LogName ‘Security’ -ComputerName $domaincontroller -In ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (:) [Get-EventLog], ArgumentException
    + FullyQualifiedErrorId : GetEventLogNoEntriesFound,Microsoft.PowerShell.Commands.GetEventLogCommand

...and here's a snippet of the relevant code:

foreach ($domaincontroller in $domaincontrollers){

Clear-Variable -name eventlog

#517,624,626,630,632,633,634,636,637,642,644,660,661,671
$eventlog = Get-EventLog -LogName ‘Security’ -ComputerName $domaincontroller -InstanceId 1102,4720,4722,4726,4728,4729,4730,4732,4733,4738,4740,4756,4757,4767 -After ((Get-Date).AddDays(-7)) | select TimeGenerated,InstanceID,Message

# ---- Members added to Domain Local Groups ----
                $MyReport += Get-CustomHeader "1" "Members added to Domain Local Groups on domain controller $domaincontroller"
                        $MyReport += Get-HTMLTable ($eventlog | Where-Object {$_.InstanceID -eq "4732"} | select TimeGenerated,Message  )
                $MyReport += Get-CustomHeaderClose

$MyReport += Get-CustomHeader0Close
$MyReport += Get-CustomHTMLClose

Thanks in advance,

Greg