For the benefit of searchers, there is another way you can produce this error message - by missing the $ off the script block name when calling it.
e.g. I had a script block like so:
$qa = {
param($question, $answer)
Write-Host "Question = $question, Answer = $answer"
}
I tried calling it using:
&qa -question "Do you like powershell?" -answer "Yes!"
But that errored. The correct way was:
&$qa -question "Do you like powershell?" -answer "Yes!"