Running powershell script inside TeamCity exits with error, but no error in console

One of my powershell build steps is having an issue that only seems to happen when run from within TeamCity. I can run the same file from a powershell console without an error.

$loadedAssembly = [System.Reflection.Assembly]::LoadFrom("C:\\powershell\\AWSSDK.dll")
$accessKeyID="1234"
$secretKeyID="1234"
$client=[Amazon.AWSClientFactory]::CreateAmazonEC2Client($accessKeyID,$secretKeyID)

The error in TeamCity is

[04:38:22][Step 2/2] T:\TeamCity\BuildAgent2\temp\buildTmp\powershell2271598119506819752.ps1 : 
[04:38:22][Step 2/2] Exception calling "CreateAmazonEC2Client" with "2" argument(s): "No 
[04:38:22][Step 2/2] RegionEndpoint or ServiceURL configured"
[04:38:22][Step 2/2]     + CategoryInfo          : NotSpecified: (:) [Write-Error], MethodInvocatio 
[04:38:22][Step 2/2]    nException
[04:38:22][Step 2/2]     + FullyQualifiedErrorId : System.Management.Automation.MethodInvocationExc 
[04:38:22][Step 2/2]    eption,powershell2271598119506819752.ps1
[04:38:22][Step 2/2]  
[04:38:22][Step 2/2] Process exited with code 1

Any help appreciated