I have been trying to install VS2010 SP1.
I have tried Using both the On-Line web-installer and Off-Line .iso file but I get the below error with either way.
ERROR MESSAGE I AM GETTING:

Does anybody know the cause of this error message?
EDIT:
Have a Look at the window comes up when i am go to=> Help=>About Microsoft Visual Studio

Based on your update I dont believe that SP1 will install on an Release candidate (your vs2010 version is RC1Rel) and you need to get a release version of Visual Studio or one of the Visual Studio Express Editions.