trying to automate browsing

I have an HTML Form like this:

<input name="member[email]" id="memberemail" style="width: 220px;" type="text" value="">
<input name="member[password]" id="memberpassword" style="width: 220px;" type="password" value="" autocomplete="off">
<input class="continue" type="submit" value="Log In">

and I have a powershell script that authenticates and browses a page: this works fine.

$username='xxx@mail.com' 
$password='<password>'




$ie = New-Object -ComObject 'internetExplorer.Application'
$ie.Visible= $true
$ie.Navigate("https://www.ksl.com/public/member/signin?login_forward=%2F")


while ($ie.Busy -eq $true){Start-Sleep -seconds 1;}   

$usernamefield = $ie.Document.getElementByID('memberemail')
$usernamefield.value = $username

$passwordfield = $ie.Document.getElementByID('memberpassword')
$passwordfield.value = $password

$Link=$ie.Document.getElementsByTagName("input") | where-object {$_.className -eq "continue"}



#<INPUT tabIndex=3 id=Logon onclick=this.disabled=true;this.form.submit(); type=submit value="Sign In">
#<input name="ctl00$pageContentPlaceHolder$btnGo" id="ctl00_pageContentPlaceHolder_btnGo" style="width: 200px;" type="submit" value="Sign In">


$Link.click()

however when I try and use it on a ASP.net page like this:

<input name="ctl00$pageContentPlaceHolder$txtUserID" id="ctl00_pageContentPlaceHolder_txtUserID" style="width: 200px;" type="text" maxlength="30" autocomplete="off">
<input name="ctl00$pageContentPlaceHolder$txtPassword" id="ctl00_pageContentPlaceHolder_txtPassword" style="width: 200px;" type="password" maxlength="256" autocomplete="off">
<input name="ctl00$pageContentPlaceHolder$btnGo" id="ctl00_pageContentPlaceHolder_btnGo" style="width: 200px;" type="submit" value="Sign In">

this modiified script doesn't fill the username and password field

$username='use000' 
$password='<password>'


$ie = New-Object -ComObject 'internetExplorer.Application'
$ie.Visible= $true
#ie.Navigate("https://fasttrng.usask.ca/Login.aspx?ReturnUrl=%2f")

while ($ie.Busy -eq $true){Start-Sleep -seconds 1;}   

$usernamefield = $ie.Document.getElementByName('ctl00$pageContentPlaceHolder$txtUserID')
$usernamefield.value = $username

$passwordfield = $ie.Document.getElementByName('ctl00$pageContentPlaceHolder$txtPassword')
$passwordfield.value = $password

$Link=$ie.Document.getElementsByTagName("input") | where-object {$_.id -eq "ctl00_pageContentPlaceHolder_btnGo"}




$Link.click()

I get

PS C:\Users\rwm132> T:\work\scripts\Untitled4.ps1

PS C:\Users\rwm132> T:\work\scripts\Untitled4.ps1

PS C:\Users\rwm132> T:\work\scripts\Untitled5.ps1
You cannot call a method on a null-valued expression.
At T:\work\scripts\Untitled5.ps1:11 char:1
+ $usernamefield = $ie.Document.getElementByName('ctl00$pageContentPlac ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
At T:\work\scripts\Untitled5.ps1:12 char:1
+ $usernamefield.value = $username
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : OperationStopped: (:) [], COMException
    + FullyQualifiedErrorId : System.Runtime.InteropServices.COMException

You cannot call a method on a null-valued expression.
At T:\work\scripts\Untitled5.ps1:14 char:1
+ $passwordfield = $ie.Document.getElementByName('ctl00$pageContentPlac ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
At T:\work\scripts\Untitled5.ps1:15 char:1
+ $passwordfield.value = $password
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : OperationStopped: (:) [], COMException
    + FullyQualifiedErrorId : System.Runtime.InteropServices.COMException

You cannot call a method on a null-valued expression.
At T:\work\scripts\Untitled5.ps1:17 char:1
+ $Link=$ie.Document.getElementsByTagName("input") | where-object {$_.i ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
At T:\work\scripts\Untitled5.ps1:22 char:1
+ $Link.click()
+ ~~~~~~~~~~~~~
    + CategoryInfo          : OperationStopped: (:) [], COMException
    + FullyQualifiedErrorId : System.Runtime.InteropServices.COMException


PS C:\Users\rwm132> 

Is there something special about the ASP.Net rendered inputs fields?

the script works for static html just not ASP.Net someone suggested that it cannot handle the AJAX part that is being presented , does that sound right? I thought webforms like this in .NET were e