preg_match() [function.preg-match]: Compilation failed: unmatched parentheses at offset 26

[eluser]Unknown[/eluser]
I am getting this error on almost every page of my site.
A PHP Error was encountered
Severity: Warning
Message: preg_match() [function.preg-match]: Compilation failed: unmatched parentheses at offset 26
Filename: libraries/Router.php
Line Number: 281

I have made some route rules as:
$route["comment/(:any)/(:any)/(:any)"]="test/comment/$1/$2/$3"

How do i fix it?
can any one help?