PRTG Custom Sensor with powershell

Dear all, I configured a powershell script which works in my PRTG testing platform installed over a windows 8 Pro with latest powershell version.

Then I translated the working script to my production server but it didn´t work there. The production PRTG server is installed over a Windows 2008 Server R2. I attach here the complete powershell script:

_________________________________________________________________
Param (
    [Parameter(mandatory=$True,Position=0)]
    [string]$Agent
)


Import-Module C:\_strap\prtgshell\prtgshell.psm1

$Oper1          = snmpget.exe -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.1.2.1.2.2.1.8.17"
$Oper2          = snmpget.exe -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.1.2.1.2.2.1.8.18"
$Oper3          = snmpget.exe -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.1.2.1.2.2.1.8.19"
$Oper4          = snmpget.exe -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.1.2.1.2.2.1.8.20"


if ($Oper1 -eq "up") { $Oper1 = 0 } `
    elseif ($Oper1 -eq "down")                   { $Oper1 = 1 } `
    elseif ($Oper1 -eq "notPresent")             { $Oper1 = 2 } `
    else                                         { $Oper1 = 3 }

if ($Oper2 -eq "up") { $Oper2 = 0 } `
    elseif ($Oper2 -eq "down")                   { $Oper2 = 1 } `
    elseif ($Oper2 -eq "notPresent")             { $Oper2 = 2 } `
    else                                         { $Oper2 = 3 }

if ($Oper3 -eq "up") { $Oper3 = 0 } `
    elseif ($Oper3 -eq "down")                   { $Oper3 = 1 } `
    elseif ($Oper3 -eq "notPresent")             { $Oper3 = 2 } `
    else                                         { $Oper3 = 3 }

if ($Oper4 -eq "up") { $Oper4 = 0 } `
    elseif ($Oper4 -eq "down")                   { $Oper4 = 1 } `
    elseif ($Oper4 -eq "notPresent")             { $Oper4 = 2 } `
    else                                         { $Oper4 = 3 }


$SwitchPorts = ($Oper1,$Oper2,$Oper3,$Oper4) -eq "0"
$ActivePorts = $SwitchPorts.Count 
$XmlOutput  = "<prtg>`n"
$XmlOutput += Set-PrtgResult "Active Ports" $ActivePorts  Active_Ports
$XmlOutput += "</prtg>"
$XmlOutput
_________________________________________________________________

If I execute this script in the powershell interface in production server I can get the following output:

PS C:\Program Files (x86)\PRTG Network Monitor\Custom Sensors\EXEXML> .\prtgshell.ps1

cmdlet prtgshell.ps1 at command pipeline position 1
Supply values for the following parameters:
Agent: 11.163.0.68
<prtg>
  <result>
    <channel>Active Ports</channel>
    <value>0</value>
    <unit>custom</unit>
    <customunit>Active_Ports</customunit>
    <showchart>0</showchart>
  </result>
</prtg>
PS C:\Program Files (x86)\PRTG Network Monitor\Custom Sensors\EXEXML>

Then in PRTG server when I add the Advanced Script, with the parameter "%host" i get the message:

Error reading response: Invalid XML (XML Parser mismatch: Wanted </<<<>, got </prtg>)

The logs of C:/program data/Paessler/Logs(Sensors) is:

The term 'snmpget.exe' is not recognized as the name of a cmdlet, function, scr
ipt file, or operable program. Check the spelling of the name, or if a path was
 included, verify that the path is correct and try again.
At C:\Program Files (x86)\PRTG Network Monitor\custom sensors\EXEXML\prtgshell.
ps1:10 char:30
+ $Oper1          = snmpget.exe <<<<  -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.
1.2.1.2.2.1.8.17"
    + CategoryInfo          : ObjectNotFound: (snmpget.exe:String) [], Command 
   NotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException
 
The term 'snmpget.exe' is not recognized as the name of a cmdlet, function, scr
ipt file, or operable program. Check the spelling of the name, or if a path was
 included, verify that the path is correct and try again.
At C:\Program Files (x86)\PRTG Network Monitor\custom sensors\EXEXML\prtgshell.
ps1:11 char:30
+ $Oper2          = snmpget.exe <<<<  -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.
1.2.1.2.2.1.8.18"
    + CategoryInfo          : ObjectNotFound: (snmpget.exe:String) [], Command 
   NotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException
 
The term 'snmpget.exe' is not recognized as the name of a cmdlet, function, scr
ipt file, or operable program. Check the spelling of the name, or if a path was
 included, verify that the path is correct and try again.
At C:\Program Files (x86)\PRTG Network Monitor\custom sensors\EXEXML\prtgshell.
ps1:12 char:30
+ $Oper3          = snmpget.exe <<<<  -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.
1.2.1.2.2.1.8.19"
    + CategoryInfo          : ObjectNotFound: (snmpget.exe:String) [], Command 
   NotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException
 
The term 'snmpget.exe' is not recognized as the name of a cmdlet, function, scr
ipt file, or operable program. Check the spelling of the name, or if a path was
 included, verify that the path is correct and try again.
At C:\Program Files (x86)\PRTG Network Monitor\custom sensors\EXEXML\prtgshell.
ps1:13 char:30
+ $Oper4          = snmpget.exe <<<<  -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.
1.2.1.2.2.1.8.20"
    + CategoryInfo          : ObjectNotFound: (snmpget.exe:String) [], Command 
   NotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException
 
<prtg>
  <result>
    <channel>Active Ports</channel>
    <value>0</value>
    <unit>custom</unit>
    <customunit>Active_Ports</customunit>
    <showchart>0</showchart>
  </result>
</prtg>

$env:path="$env:Path;C:\Program Files\net-snmp" #this line goes to the very top of your script

$Oper1 = snmpget.exe -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.1.2.1.2.2.1.8.17"

$Oper1 = (snmpget.exe -Ovq -r 3 -v 2c -c teldat $Agent ".1.3.6.1.2.1.2.2.1.8.17")