What does this error mean

[eluser]hogofwar[/eluser]
I keep getting this error :

Code:

Fatal error: ob_start() [<a href='ref.outcontrol'>ref.outcontrol</a>]: Cannot use output buffering in output buffering display handlers in *snipped*/system/libraries/Exceptions.php  on line 162

what does it mean and how can I fix it?

if you need any more information please just ask, this error is driving me crazy!