Object Reference Exception in SharePoint Installer

We got the same error, I got the follwing solution from a blog and this solved our problem:

After checking the SolutionID GUID in the Setup.exe.config file with the SolutionId GUID in my project manifest.xml file, I realized that they were different. I created a new GUID  (just for peace of mind) and updated both SolutionIds. Before I could run setup again, I had to delete the wsp from the Sharepoint solution store. I ran this bat file to do so
(taken from Ted Pattison's WSS401 lab)

@SET STSADM="c:\program files\common files\microsoft shared\web server extensions\12\bin\stsadm.exe"

%STSADM% -o retractsolution -name YourSilverlightApplication.wsp -immediate

%STSADM% -o execadmsvcjobs

%STSADM% -o deletesolution -name YourSilverlightApplication1.wsp

Feature Scope Error:

http://social.technet.microsoft.com/Forums/en-US/sharepointadmin/thread/dd328fce-6d16-434f-b4bf-a53deac8eaad/

Info:
http://arcadiaunlimited.com/blog/tag/sharepoint-solution-installer/

STSADM:
http://www.codebanking.com/articles/sharepoint/sharepoint-stsadm-command-for-deployment.asp