Why am I not allowed to save a file with an Admin account?

Question

I'm right to administrate the cpu (a tick in the box of user account), but I'm not allowed to save a file (like php.ini or .bash_profile when opened with textmate or textEdit, even using nano). Does anyone have some ideas about that? May I have a hint or a link toward a result?
Thank you for your help,
Patweb
OSX 10.6.8 on new iMac 27" (last generation)

Answer 1

The php.ini file can be accessed by various file paths, including via its traditional /etc/php.ini location and by the /private/etc/php.ini path referenced in this thread, and this is a protected system directory, and the files in this location can only be modified with root access (whether via sudo or with the root user when enabled) or by reconfiguring the access control lists or protections on the files and directories to allow access.
To locate the file, use the locate command:
$ locate php.ini
/private/etc/php.ini
/private/etc/php.ini.applesaved
/private/etc/php.ini.default
/private/etc/php.ini.server-default
$
For details on the Mac directory and file structure layout, there is a write-up here; that goes into the various directories that exist on Mac OS X and Mac OS X Server.
While I am well aware a user should not require sudo to access files in a user's home directory, there are cases where a user is accessing .bash_profile in other users' directories, and this too can require sudo.   I've also encountered mis-protected login directories, though these are less common.
The setup that OP was encountering appeared to be triggered by standard system security, and these sorts of details are discussed in the security manuals for the various releases, as well as the directory and file system link above.