PowerShell form not displaying when screen is locked - forms

Question

I'm using a PowerShell form to prompt users to close down Adobe Reader so it can be upgraded. It's executed via SCCM, so runs in the System context. It works if the user is logged on and the session is active, but if the screen is locked, the form does not display when I unlock the screen, although the script is running.
I originally used $Form.ShowDialog() to display it but saw some other posts that said it wasn't reliable, so I switched to [void][System.Windows.Forms.Application]::Run($Form) but it still doesn't work. Can anyone help me fix this please?
Below is the trimmed-down script with only the code relevant to rendering the form.
Add-Type -AssemblyName System.Windows.Forms, System.Drawing
$Font = New-Object System.Drawing.Font('Segoe UI Light',14,[System.Drawing.FontStyle]::Regular)
$FontBold = New-Object System.Drawing.Font('Segoe UI',13,[System.Drawing.FontStyle]::Bold)
Function EndForm
{
$Timer.Stop();
$Timer.Dispose();
$Label.Dispose();
$CountdownLabel.Dispose();
$ProgressBar.Dispose();
$OKButton.Dispose();
$Form.Close();
$Form.Dispose();
}
$OnOKClick =
{
$MsgBoxInput = [System.Windows.Forms.MessageBox]::Show("Are you sure you want to close and uninstall Adobe Reader now?","Confirm Adobe Reader Removal","YesNo","Warning")
If ($MsgBoxInput -eq "Yes") {EndForm}
}
$Script:Countdown = 3600
$OKToolTip = "Click OK to close and uninstall Adobe Reader now"
$CountdownSubtitle = "Adobe Reader will close and uninstall in"
$Label = New-Object System.Windows.Forms.Label
$Label.AutoSize = $False
$Label.Height = 120
$Label.Width = 630
$Label.Font = $Font
$Label.BackColor = "White"
$Label.ForeColor = "#4D4C5C"
$Label.Location = New-Object System.Drawing.Size(52,180)
$Label.Text = "Your computer will soon be upgraded to newer versions of Windows 10 and Office 365. In order to succeed, the upgrade process requires that Adobe Reader be closed and uninstalled first. It will not be available for use again until after the upgrade has completed."
$CountdownLabel = New-Object System.Windows.Forms.Label
$CountdownLabel.AutoSize = $False
$CountdownLabel.Height = 40
$CountdownLabel.Width = 530
$CountdownLabel.Font = $Font
$CountdownLabel.BackColor = "White"
$CountdownLabel.ForeColor = "#4D4C5C"
$CountdownLabel.Location = New-Object System.Drawing.Size(120,380)
$ProgressBar = New-Object System.Windows.Forms.ProgressBar
$ProgressBar.Location = New-Object System.Drawing.Size(52,340)
$ProgressBar.Size = New-Object System.Drawing.Size(635,35)
$ProgressBar.Style = "Continuous"
$ProgressBar.Maximum = $Script:Countdown
$ProgressBar.Minimum = 0
$OKButton = New-Object System.Windows.Forms.Button
$OKButton.Name = "OK_Button"
$OKButton.Size = New-Object System.Drawing.Size(80,40)
$OKButton.Location = New-Object System.Drawing.Size(330,450)
$OKButton.UseVisualStyleBackColor = $True
$OKButton.Text = "OK"
$OKButton.DataBindings.DefaultDataSourceUpdateMode = 0
$OKButton.Add_Click($OnOKClick)
$ToolTip = New-Object System.Windows.Forms.ToolTip
$ToolTip.IsBalloon = $False
$ToolTip.InitialDelay = 100
$ToolTip.ReshowDelay = 200
$ToolTip.SetToolTip($OKButton,$OKToolTip)
$Form = New-Object System.Windows.Forms.Form
$Form.Text = "Contoso LLC"
$Form.Font = $Font
$Form.Width = 770
$Form.Height = 580
$Form.MinimizeBox = $False
$Form.MaximizeBox = $False
$Form.ControlBox = $False
$Form.ShowIcon = $False
$Form.WindowState = "Normal"
$Form.FormBorderStyle = "Fixed3D"
$Form.ShowInTaskbar = $True
$Form.StartPosition = "CenterScreen"
$Form.Topmost = $True
$Form.Controls.Add($ProgressBar)
$Form.Controls.Add($Label)
$Form.Controls.Add($CountdownLabel)
$Form.Controls.Add($OKButton)
$Timer = New-Object System.Windows.Forms.Timer
$Timer.Interval = 1000
$Timer.Add_Tick(
{
If ($Script:Countdown -eq 0) {EndForm}
$ProgressBar.Value = $Script:Countdown
$TimeRemain = New-Timespan -Seconds $Script:Countdown
$HrsRemain = $TimeRemain.Hours
$MinsRemain = $TimeRemain.Minutes
$SecsRemain = $TimeRemain.Seconds
If ($HrsRemain -ge 2) {$HrsText = "$HrsRemain hours"}
If ($HrsRemain -eq 1) {$HrsText = "$HrsRemain hour"}
If ($MinsRemain -ge 2) {$MinsText = "$MinsRemain minutes"}
If ($MinsRemain -eq 1) {$MinsText = "$MinsRemain minute"}
If ($SecsRemain -ge 2) {$SecsText = "$SecsRemain seconds"}
If ($SecsRemain -eq 1) {$SecsText = "$SecsRemain second"}
$CountdownLabel.Text = "$CountdownSubtitle $HrsText $MinsText $SecsText"
If ($HrsRemain -ge 1 -And $MinsRemain -eq 0) {$CountdownLabel.Text = "$CountdownSubtitle $HrsText $SecsText"}
If ($HrsRemain -eq 0) {$CountdownLabel.Text = "$CountdownSubtitle $MinsText $SecsText"}
If ($HrsRemain -eq 0 -And $MinsRemain -eq 0) {$CountdownLabel.Text = "$CountdownSubtitle $SecsText"}
$Script:Countdown--
})
$Timer.Start()
[void][System.Windows.Forms.Application]::Run($Form)

Answer 1

I have decided to 'work around' this issue by detecting for the presence of the logonui process, which means the screen is locked. In that case, I will just close Adobe Reader anyway.