Smarty Error

[Anniem]

Hai Team,

I keep seeing this following error in my whmcs activity log :

Smarty Error: Syntax error in template "mailMessage:mailMessage:message" on line 4 "<p>Order Number: {<strong>$order_number</strong>}</p>" - Unexpected "<" - User ID: 

Am not able to locate the file that triggers the error for debugging the error.  Any idea on how this can be done or on the error?? 

Regards,

Annie