Hmm interesting. I checked with Debug on and am not getting the error and the code looks fine to me so this must be related to a connectivity issue. ie the connection to the AITpro API Server dropped out/or hiccuped/or the MySQL DB Query hiccuped during the Cron check for an upgrade to BPS Pro. Basically the reponse came back as empty so there was nothing to unserialize.
But i did find these 2 nick nack things that need to be corrected. Oops. variables, variables - dot your I's and cross your T's LOL. ;) These are syntax minor issues and will not cause any problems. Just nick nacks that I just fixed. ;)
[28-Sep-2012 00:31:43 UTC] PHP Notice: Undefined index: SUHOSIN_PATCH in C:\xampp2\xxxxxxx\xxxxxxxxxx\wp-content\plugins\bulletproof-security\admin\options.php on line 1587
[28-Sep-2012 00:32:22 UTC] PHP Notice: Undefined variable: filename in C:\xampp2\xxxxxxx\xxxxxxxxxx\wp-content\plugins\bulletproof-security\admin\quarantine\quarantine.php on line 153