Powershell Archive script win2008r2 problems - powershell

Question

I created a ps-script to move MS SCCM backup folder to another location and delete folders older than 2 days :
$Date = Get-Date -format d.M.yyyy
$BackupDir = "\\Source_Servername\Folder1\Folder2"
$ArchiveDir = "\\Destination_Servername\Folder1\Folder2"
set-alias 7za "$ArchiveDir\7za.exe"
Get-Item "$ArchiveDir\*" |? {$_.psiscontainer -and $_.lastwritetime -le (get-date).adddays(-2)} |% {remove-item $_ -Recurse -Confirm:$false}
7za a -r "$ArchiveDir\$Date\$BackupDir.7z" $BackupDir
I created this using Win 8 and when i try to apply it on win2008r2 servers it fails with the following error :
Bad numeric constant: 7.
At E:\xxxxx\xxxxx\xxxx\Afterbackup.ps1:9 char:2
+ 7 <<<< za a -r "$ArchiveDir\$Date\$BackupDir.7z" $BackupDir
+ CategoryInfo : ParserError: (7:String) [], ParseException
+ FullyQualifiedErrorId : BadNumericConstant
It works when i enter the full path to 7za.exe like this :
\Destination_Servername\Folder1\Folder2\7za a -r "$ArchiveDir\$Date\$BackupDir.7z" $BackupDir
I'm new to powershell so i would appriciate any help :)

Answer 1

PowerShell v1 & v2 do not like commands that start with numbers. The issue seems to have been addressed in v3 and that's probably why it works on your workstation. You can work around this by placing a backtick in front of the alias when you execute it:
`7za a -r "$ArchiveDir\$Date\$BackupDir.7z" $BackupDir
Alternately, you can change the alias to not start with a number.