Hi Stive,
about this problem with extracting the DRA installer from what you've described, it seems like the system is having trouble finding a specific file it needs to continue with the installation. This kind of error usually pops up when either the installer package isn't complete or maybe the script is looking in the wrong place for what it needs.
First thing I'd suggest is checking that folder at C:\dr\DRAppliance\ to make sure all the necessary files are actually there. Sometimes during downloads things can get interrupted or files might not extract properly. The PushInstallAgentSetup.msi should be there along with some other supporting files. If anything looks missing, you might need to redownload the appliance package from the Azure portal. Microsoft has a good guide on getting the right files here: Download Azure Migrate Appliance.
Another thing to try is running the script again but this time make sure you're opening PowerShell as an administrator. Right click on it and select "Run as administrator" - sometimes that extra permission level helps with accessing everything the script needs. Also worth checking that your antivirus isn't accidentally blocking anything - those security programs can sometimes be a bit overprotective with installer files.
If you're still seeing the same error, there might be some clues in the log files. You can usually find more detailed error messages in C:\ProgramData\Microsoft Azure\Logs or by checking the Windows Event Viewer under Applications and Services Logs. The exact file name that's missing might be listed there which would help track down what's going wrong.
Don't worry if this feels a bit overwhelming - these setup processes can have a few tricky steps but we'll get through it. Let me know how these suggestions work out.
rgds,
Alex