Update your CWM version in ROM manager.
It should be the top choice when you open ROM Manager - update Clockwork Recovery.
Make sure you have ample space on a FAT32 formatted SD card, as well a the minimum radio(s) required for CM.
Prior to flash, in recovery, make sure you wipe data/factory reset and clear cache - also go into advanced and format system.
Post back your results and we'll go from there.
LG G2 - Malladus 1.2.2
Nexus 7 (2012) ~ Prime
Galaxy Nexus ~ Retired
Thunderbolt - ~ Retired | OG Incredible ~ Retired
46" Sony Google TV ~ Honeycomb | Kindle Fire ~ Rooted