Thanks. I actually was aware of the different things that could cause the blank screen. I'm trying to narrow down which file might be missing or have a syntax error. The debug info isn't very helpful. It says:

PHP Warning: Cannot modify header information - headers already sent by (output started at /PATH_TO_STORE/includes/languages/english/subito2/index.php:62) in /PATH_TO_STORE/includes/functions/functions_general.php on line 45

I actually didn't make any edit to either of those files and I don't find any syntax error in looking at either of them. So, I'm still trying to determine which includes are used when a category has only one product in it instead of several.