Restoring CWM backup leads to splash loop

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http://forum.xda-developers.com – I'm using: NexusHD2-ICS-4.0.4-CM9-HWA V2.4 Something went wrong on my phone so I decided to restore a backup. I had one from 2 weeks ago. After the restore completed, I rebooted my phone. It was stuck on the ROM splash screen and never got past that. I left it running for 20 minutes. I tried clearing /cache and dalvik-cache, with no luck. If I format /data then it works, but then of course all my data is gone. Luckily I had a previous backup which did work. I'm nervous about nandroid backup/restore. Can I trust it? It only happened for this particular backup, but why would it happen a (HowTos)