iRule error undefined procedure

I received an error when attempting to create this iRule. The error was "undefined procedure &160][ ]". When I searched the forums I found other posts where the error indicated an invalid command; although I do not notice an invalid command in this iRule. Any suggestions would be helpful.

when HTTP_REQUEST { if { [SSL::cert count] > 0 } then { set clientcert [SSL::cert 0] set clientdn [X509::subject [SSL::cert 0]] set clientserial [X509::serial_number [SSL::cert 0]] HTTP::header insert XClientCert [b64encode $clientcert] HTTP::header insert XClientDN $clientdn HTTP::header insert XClientSerial $clientserial } }