I'm with orangechoochoo here! If you are getting the error messages, it merely reports the first one (so checksum on build.prop failing) but if you modified build.prop, you may well have modified other files as well, and you will need to request these files as well. Since you are going to update anyway, there is nothing that needs preserving, so either flash GB and then the update should work (if you really want to get the update OTA for some reason) or install ICS directly.How do you guys know the build.prop is your problem, and how do you know it's your only problem?
Just flash 219 and then check and download the update, or just RSDLite ICS. This way you'll get ICS and you won't be spending your time hunting down the problem.