Check the following paragraph:
& 'C:\Program Files\ownCloud\owncloud.exe' --logfile - --logflush | Write-Host
Make sure to copy the command as is, with leading ampersand and single quotes around the path and logfile pointing to
This should then output the whole error message. I would suspect that an old ownCloud installations configuration directory still exists and points to a drive/folder that no longer exists. I think the error message should also tell in which path this configuration is.