Unable to cast COM object of type 'Microsoft.SharePoint.Library.SPRequestInternalClass' to interface type 'Microsoft.SharePoint.Library.ISPRequest'.

I was working with PowerShell and Sharepoint 2010 and for some reason I have got this error:

Unable to cast COM object of type 'Microsoft.SharePoint.Library.SPRequestInternalClass' to interface type 'Microsoft.SharePoint.Library.ISPRequest'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{BDEADEBE-C265-11D0-BCED-00A0C90AB50F}' failed due to the following error: Bad variable type. (Exception from HRESULT: 0x80020008 (DISP_E_BADVARTYPE)).

This is the only stuff I was doing was adding a new library to my existing site. This is the code:

 [void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")
 $listTemplate = [Microsoft.SharePoint.SPListTemplateType]::DocumentLibrary
 $spWeb = Get-SPWeb -Identity "http://sp_foundation_g/sites/Documents"
 $spWeb.Lists.Add("AllDocuments","My Doc Library",[Microsoft.SharePoint.SPListTemplateType]::DocumentLibrary)

If you use Powershell you normally are administrator, but just in case I decided to check RunWithElevatedPrivileges in order to avoid any problem with the security. Everything was fixed straight away, and I didn’t get the error anymore, even if I tried to run the code without RunWithElevatedPrivileges. This is the code I ran to fix it:

[Microsoft.SharePoint.SPSecurity]::RunWithElevatedPrivileges(  
 {      
     [void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")
     $listTemplate = [Microsoft.SharePoint.SPListTemplateType]::DocumentLibrary
     $spWeb = Get-SPWeb -Identity "http://sp_foundation_g/sites/Documents"
     $spWeb.Lists.Add("AllMydocuments","My Doc Library",[Microsoft.SharePoint.SPListTemplateType]::DocumentLibrary)
 }
)  

Conclusion: I have done plenty of research but I can’t find the answer of why this is happening, but the good news, it can be fixed!.