Thread: How to customize error messages?

How to customize error messages?

Hi,
There are a few message errors that my users are getting that I would like to change / modify, but I am not sure of how to go about this.
For example, Error #1:
--When an ad is accidentally turned off by the user in the Dashboard, when they click on the pencil icon to edit the listing, they get the error message:
"You have entered an invalid ad id or do not have permission to edit that ad."
Instead, I would like to add something about the fact that they need to make the ad live to edit it. I am somewhat comfortable editing CSS, etc. but have little knowledge on how to edit .php files. How would I find / customize this error message?
Example #2:
I have also noticed that when a search turns up no results, there is no message for the user, just blank space below the header "Search Results". I would like to put some kind of message there that at least says "We're sorry...no search results were found for this keyword. Please try your search using a different keyword, or try your search again later."... or something to that effect. How would I do this?
Thanks,
Rachel