That's exactly why I asked you if you were in your home folder denoted by ~ before the $ prompt or you are in /home/user/MyDocs.

These are basically part of two separate file systems. /home/user becomes part of /home which is ext2. So changing file permissions will work there. However, /home/user/MyDocs is a VFAT file system. Changing file permissions will not work there.

Do one simple example:

In your ~ folder (/home/user) create a file as:

Then, change the file permissions:

You will see that the file permissions have changed as rwxrwxrwx

Now cd to /home/user/MyDocs and repeat this procedure. The file created there will have permissions -rw-r--r--. Also the group owner will be root and not users. If you try chmod 777 on the tmp_file here the permissions will still remain as -rw-r--r--.