Script Only Runns Sucessfully 50-60% of the time - powershell

Question

I'm sending a zip and the powershell script to computers in our organisation through our management software and then executing the powershell script through command prompt. The script unzips the folder, installs a program and adds some registry keys to the registry.
If the machine doesnt say that a policy is preventing execution of the script, it runs as expected, the program is installed and the registry keys are imported. But if it does give the warning and I set the policy to unrestricted I get the below error error. I am on Windows 8.1 and using Powershell 4.0
Id not be found.
At C:\Temp\tps1.ps1:5 char:9
+ Add-Type <<<< -assembly "system.io.compression.filesystem"
+ CategoryInfo : ObjectNotFound: (system.io.compression.filesyste
m:String) [Add-Type], Exception
+ FullyQualifiedErrorId : ASSEMBLY_NOT_FOUND,Microsoft.PowerShell.Commands
.AddTypeCommand
Add-Type : Cannot add type. One or more required assemblies are missing.
At C:\Temp\tps1.ps1:5 char:9
+ Add-Type <<<< -assembly "system.io.compression.filesystem"
+ CategoryInfo : InvalidData: (:) [Add-Type], InvalidOperationExc
eption
+ FullyQualifiedErrorId : ASSEMBLY_LOAD_ERRORS,Microsoft.PowerShell.Comman
ds.AddTypeCommand
Unable to find type [io.compression.zipfile]: make sure that the assembly conta ining this type is loaded.
At C:\Temp\tps1.ps1:7 char:25
+ [io.compression.zipfile] <<<< ::ExtractToDirectory($BackUpPath, $destination) + CategoryInfo : InvalidOperation: (io.compression.zipfile:String
) [], RuntimeException
+ FullyQualifiedErrorId : TypeNotFound
anyone have any ideas?

Answer 1

on systems where .NET 4.5 is not installed, use:
$BackUpPath = "C:\Temp\Install.zip"
$Destination = "C:\Temp"
$shell_app=new-object -com shell.application
$zip_file = $shell_app.namespace($BackUpPath )
$destination = $shell_app.namespace($Destination )
$destination.Copyhere($zip_file.items(),0x4)
on systems with.NET 4.5 use:
Add-Type -assembly "system.io.compression.filesystem"
[io.compression.zipfile]::ExtractToDirectory($BackUpPath, $destination)
A script on technet combines the above 2 methods.
On PowerShell V5 , this is much simplified:
Expand-Archive $BackUpPath -destination $Destination
there are other ways to unzip files using 3rd party libraries such as 7-zip, etc but that creates a dependency.
Note: Powershell execution policies can be set using group policy. see link here