powershell invoke-command does not work if I use -computerName

I want to execute below code in the either local or remote machine whith current user.

$BackUpSqlAgentAndRemoveOldbackup = {
    param([string]$AppServer,[string]$SqlInstance,[string]$BackupShare,[string]$alias)

    [Environment]::UserName #I got same user name in all cases.

    [System.Reflection.Assembly]::LoadWithPartialName('Microsoft.SqlServer.Smo') | Out-Null

    $server = New-Object ('Microsoft.SqlServer.Management.Smo.Server') $SqlInstance

    $backupName = 'SqlAgentJob_' + $SqlInstance + '_' + (Get-Date –format ‘yyyyMMdd_HHmm’) + '_' + $alias + '.sql'
    $backupPath = join-path $BackupShare $backupName

    $oldBackups = Get-ChildItem $backupShare | where { ( $_.name -like 'SqlAgentJob_*.sql' ) }
    $server.JobServer.Jobs.Script() | Out-File -filepath $backupPath
    foreach ( $item in $oldBackups ) { remove-item $item.fullName }
}

the @argList is

@('hafcapp-1', 'hafcsql-1', '\\Host5FileSrv\Backup\test','auto')

I notice that

this one, it works well (no -comupterName and -session)

Invoke-Command -ScriptBlock $BackUpSqlAgentAndRemoveOldbackup -argumentList $argList

this one, it throw execption (I also tried "-session", get same result)

Invoke-Command -computerName localhost -ScriptBlock $BackUpSqlAgentAndRemoveOldbackup -argumentList $argList

the exception is as below, it seems the it can not access the folder.

Cannot find path '\\Host5FileSrv\Backup\test' because it does not exist.
    + CategoryInfo          : ObjectNotFound: (\\Host5FileSrv\Backup\test:String) [Get-ChildItem], ItemNotFoundException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetChildItemCommand

You cannot call a method on a null-valued expression.
    + CategoryInfo          : InvalidOperation: (Script:String) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

Cannot bind argument to parameter 'Path' because it is null.
    + CategoryInfo          : InvalidData: (:) [Remove-Item], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorNullNotAllowed,Microsoft.PowerShell.Commands.RemoveItemCommand

does anyone know how can I do if I want to add computerName or session? (notes:[Environment]::UserName return identical user)