Powershell step cannot find file specified

[tan125]

I'm running VBP 6.7 and am trying to use the PowerShell step to alphabetize a list by putting the following into the Powershell script window:

$abcList = (get-content %PROJDIR%\CompareFiles_%BASELINE_VERSION%.txt) | sort-object

$abcList | out-file -filepath %PROJDIR%\CompareFiles_%BASELINE_VERSION%.txt

(Above, BASELINE_VERSION is an integer and PROJDIR is a path on the D: drive.)

If I run these lines from the Powershell command line, it works fine. But when running from the Powershell action in VBP, I get "Failed to create process: The system cannot find the file specified."

Any ideas?