When using System Center Data Protection Manager 2007 or 2010 (DPM) to backup your production servers, you might encounter a situation where the recovery point volumes for your protected data source keep running out of space and the number of days that DPM has recovery points for exceeds the desired retention range. If you run vssadmin list shadows, or run diskshadow.exe followed by list shadows all command, you can see that there are more shadow copies than there should be based on the desired retention goal. Also, if you manually run the DPM Power Shell pruneshadowcopies2010.ps1 script, no recovery points are removed, but there are no errors.
So what’s going on here? Most likely this is happening because the NetBIOS name of the DPM server is longer than 15 characters.
Resolution
To resolve the problem perform the following to truncate the name to the 15 character limit.
1) Using notepad, open C:\Program Files\Microsoft DPM\DPM\bin\pruneshadowcopiesDpm2010.ps1 (For DPM2010) or pruneshadowcopies.ps1 (For DPM 2007).
2) Locate the following entry:
$dpmservername = &"hostname"
3) Replace the &"hostname" with the truncated 15 character NetBIOS name of the DPM server. For example, if the DPM Server’s host name is "Long-DPM-server-name" then modify the entry as follows:
$dpmservername = "ward-dpm01.wardvissers.local"
4) Save the modified script.
5) Either run the script manually, or wait for it to run at midnight – then verify the shadow copies are being pruned as expected.
Now I have nice Green Protection Groups 
Special Thanks to J.C. Hornbeck