What is causing this error :- Restore-SPSite : 0x80070003

I want to restore a site collection to my staging environment , and when i typed the following power shell command :-

PS H:\> Restore-SPSite http://ggvstg01:12160/discussionforum/GeneralDiscussi
    -Path C:\Users\user\Desktop\Backup\GeneralDiscussion.bak -Force

Confirm
Are you sure you want to perform this action?
Performing operation "Restore-SPSite" on Target"http://ggvstg01:12160/discussionforum/GeneralDiscussion".
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help
(default is "Y"):y

I will get the following error :-

**Restore-SPSite : <nativehr>0x80070003</nativehr><nativestack></nativestack>
At line:1 char:1+ Restore-SPSite http://ggvstg01:12160/discussionforum/GeneralDiscussion
-Pat ...+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~+ CategoryInfo          : InvalidData: (Microsoft.Share...dletRestoreSite:
   SPCmdletRestoreSite) [Restore-SPSite], DirectoryNotFoundException+ FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SPCmdletRestoreS
   ite**