ERROR: Couldn't Find BOOTMGR while booting BackTrack via Bootable pendrive

I was trying to boot my machine with Backtrack via bootable pendrive, but unfortunately I got an error by saying

Couldn't Find BOOTMGR

No need to worry, It has just not found the boot loader. so we will have load that by the command. Just write the following command and it will be start loading

boot: /casper/vmlinuz boot=casper initrd=/casper/initrd.gz text splash vga=791    

now your machine will be start booting with backtrack via your pen drive.