Session Unserialize Error

[eluser]Clooner[/eluser]

Code:

ERROR - 2009-11-05 07:04:52 --&gt; Severity: Notice  --&gt; unserialize() [<a href='function.unserialize'>function.unserialize</a>]: Error at offset 176 of 176 bytes /system/libraries/Session.php 708

I often see this error coming by in the log files. Any ideas on what and how. My app seems to work fine but sometimes this error pops up in the log files. It seems to happen only with bots and not normal browsers but I'll have to double check this to be sure.