If you do not use an os from your carrier for your berry and want to load a hybrid or what ever you need to remove a file (vender.xml) for the os to work right
Actually, it is so the OS can be recognized as valid by the Apploader wizard. If you leave the vendor.xml file in there, and the OS is from a carrier that is different from your BB, then Apploader will ignore the OS software and won't give you the option to load it.
I had the same problem with my sprint blackberry and I took it to the sprint store, they tried to fix it but they couldn't so they just gave me a new one