Cars Race o Rama seems to be the first Xbox 360 game with the 'Wave 4'. Basically, Wave 4 is Wave 3 with the new 8498 NXE update.
Because iXtreme v1.6 checks the video partition CRC (for security) to only boot Wave1/2/3, it will not be able to boot the new Wave4 discs.
There are several solutions ... you can downgrade to iXtreme v1.51 (that was made when Wave 3 was released) that does not check the Video partition CRC and if you must use iXtreme v1.6 (liteon drive) you can use the activate.iso boot-disc that will bypass this check for you.
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Because iXtreme v1.6 checks the video partition CRC (for security) to only boot Wave1/2/3, it will not be able to boot the new Wave4 discs.
There are several solutions ... you can downgrade to iXtreme v1.51 (that was made when Wave 3 was released) that does not check the Video partition CRC and if you must use iXtreme v1.6 (liteon drive) you can use the activate.iso boot-disc that will bypass this check for you.