Have a look at http://drupal.org/project/variablecheck which has a D7 version as well as D6. This solved a problem for me on a D6 site that I couldn't track down any other way. Hope it works for you too.
Mike
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From: Ursula Pieper [mailto:dramamezzo@gmail.com] Sent: 30 March 2011 02:55 To: support@drupal.org Subject: [support] messed up variable?
I moved my sites to a different host (aside: VPS makes a big difference over shared hosting!), and for one of the sites, I get this error message until the cache is built, and then again after clearing the cache:
Notice: unserialize() [function.unserialize]: Error at offset 2 of 21 bytes in variable_initialize() (line 749 of myhomedirectory/www/includes/bootstrap.inc).
I searched the web, but didn't find anything that could help me. Any suggestions on how to find the problem? I am running drupal 7, and have listed the installed modules below.
Thanks, Ursula
Backup and Migrate 7.x-2.1 7.x-2.1 Up to date Drupal core 7.0 7.0 Up to date CAPTCHA 7.x-1.0-alpha2 7.x-1.0-alpha2 Up to date Chaos tool suite 7.x-1.0-alpha4 7.x-1.0-alpha4 Up to date Date 7.x-1.0-alpha2 7.x-1.0-alpha2 Up to date Google Analytics 7.x-1.2 7.x-1.2 Up to date Link 7.x-1.0-alpha3 7.x-1.0-alpha3 Up to date Location Map 7.x-1.0 7.x-1.0 Up to date Meta tags quick 7.x-1.2 7.x-1.2 Up to date Page Title 7.x-2.4-beta1 7.x-2.4-beta1 Up to date Pathauto 7.x-1.0-beta1 7.x-1.0-beta1 Up to date Redirect 7.x-1.0-beta1 7.x-1.0-beta1 Up to date Token 7.x-1.0-beta1 7.x-1.0-beta1 Up to date Views 7.x-3.0-beta3 7.x-3.0-beta3 Up to date Zen 7.x-3.x-dev 7.x-3.x-dev Up to date