win32_process create fails with Unknown failure for service account user

I have a windows service account user, using which i'm trying to create a background process using the WMI win32_proces. But fails with Unknown Failure. (Tried this with administrator, nonadmin, domain admin, domain nonadmin users. works fine)

$process = [WMICLASS]"\\$computername\ROOT\CIMV2:win32_process"
$processinfo = $process.Create("powershell.exe -WindowStyle Hidden test.ps1")
Write-Host $processinfo.returncode