Could be a few things…the simplest is that sometimes PowerShell behaves differently when run in 32-bit mode (the default), so try adding
action uses wow64 redirection false
anywhere in the actionscript before running the ‘waithidden’ command.
There can also be some differences in how quoting works. If you’re up for it, I’d try using the native PowerShell script type (if you’re on BigFix 10.0.3 or higher), or download and try our preview “Script Task Builder” dashboard described at New BigFix Labs Dashboards
The Dashboard generates a PowerShell script and executes it on-the-fly, and can save the output to a text file so at least if there’s an error message you can get some indication of what’s happening.