Help with Chmod

Hi guys I am running the following:
Using a site app on one domain to change permissions on another site on the same box as my admin app. Then uploading dirs and files to the 2nd site before changing permissions back.

The 2nd domain is 0750 and I am trying to get it to 0777 but get the following:
Warning: chmod() [function.chmod]: Operation not permitted in XXXXX

When I manually change permissions to 0777 the mkdirs and file copies works fine but i just cannot get chmod to work.

Can someone please explain what a user/owner is and how to find out if this possible on my VPS. Would this even be the cause of the problem?

Why would the operation not be permitted?

Thanks for your help.
Regards
D.

The only reason I can see that would happen is if you are not root. Also I would drop the 0 and just use:

chmod 777 filename

To give an entire directory and all subdirectorys and files 777 use:

chmod -R 777 directory

Are you sure you want to give read/write/execute privledges to everyone?

There is a very good site here:
http://www.csgnetwork.com/csgchmodcalc.html

It will tell you exactly what permissions to use.