Today I got an UnauthorizedAccessException when running the following script in powershell

Invoke-WebRequest -Uri $url `
     -UseDefaultCredentials `
     -UseBasicParsing ` 
     -Method Post `
     -ContentType 'application/json' `
     -InFile data.json 

There was no logging on the webserver, there was no access-denied message, there was no traffic at all. What happend?
Turns out the problem was the file (data.json) was readonly. So I added the following step to remove the readonly flag.

Set-ItemProperty data.json -name IsReadOnly -value $false

Now my post to the webservice succeeds.