I'm attempting to move from

http://domain.site.com/folder/profile.php?name=some_person

towards the cleaner URL

http://sub1.site.com/folder/some_person

During my .htaccess I've the appropriate section:

#Prevent from overriding actual directories and files

RewriteCond %{SCRIPT_FILENAME} !-d  
RewriteCond %{SCRIPT_FILENAME} !-f 

# Rewrite user URLs
#   Input:  folder/NAME/
#   Output: profile.php?name=NAME
RewriteRule ^folder/(\w+)/?$ profile.php?name=$1

However, if Time passes to

http://sub1.site.com/folder/fred

for example (where fred is really a valid user), I recieve 404 page not found error

What shall we be held doing wrong? Thanks!

Improve your last line to:

RewriteRule ^folder/(\w+)/?$ profile.php?name=$1

BTW, you did not mention the domain title within the result, your present domain and also the result domain will vary, I suppose it is a mis-typo but when you believe it isn't then please try the next rule.

Do this:

RewriteEngine On
RewriteCond %{SCRIPT_FILENAME} !-d  
RewriteCond %{SCRIPT_FILENAME} !-f 
RewriteCond %{HTTP_HOST} ^sub1.site.com$
RewriteCond %{REQUEST_URI} ^/folder
RewriteRule ^/folder/(\w+)/?$ http://domain.site.com/folder/profile.php?name=$1 [QSA]

Note: If you feel domain is same, then just take away the domain in the rule.

You are able to validate your rewrite-rule within this link: http://martinmelin.se/rewrite-rule-tester/