I have used Core FTP for years and have never come upon this problem hope someone can help.
I am trying to override index.html on my website but keep getting the message "550 index.html: Operation not permitted" and cannot even delete the index.html.
I can upload any other file or override any other file.
this is the message in my FTP

DTM index.html
213 20101208101912
File exists, prompting user...
index.html overwritten...
TYPE A
200 Type set to A
PASV
227 Entering Passive Mode (202,146,213,3,249,27).
STOR index.html
Connect socket #940 to 202.146.213.3, port 63771...
550 index.html: Operation not permitted
index.html - 0 bytes transferred
PASV
227 Entering Passive Mode (202,146,213,3,249,28).
LIST
Connect socket #896 to 202.146.213.3, port 63772...
150 Opening ASCII mode data connection for file list
226 Transfer complete
DTM index.html
213 20101208101912
File exists, prompting user...
index.html Aborted...
Transfer time: 00:00:08
PASV
227 Entering Passive Mode (202,146,213,3,195,207).
LIST
Connect socket #952 to 202.146.213.3, port 50127...
150 Opening ASCII mode data connection for file list
226 Transfer complete
Transferred 20,841 bytes in 0.125 seconds
thanks for your help.

If you cannot change the permissions (chmod) of the file in question to 777 and then try to delete it, it means that the server does not allow you to edit/change permissions/delete said file.

You need to contact your server administrator or hosting support to correct this.

thanks for that no cannot change it and can't delete it neither will contact the server

No problem. It will be interesting to know what they said, please let us know.

Good luck

Well finally fixed, the host had locked the files (but only the index.html) for added security what a stupid thing to do. They have no idea thanks for your input.

Glad you got sorted. Personally, I can not see the reasoning behind locking the index.html file, as this just don't make sense to me.

And because the website was run from a subfolder (which I didn't know as it wasn't my website) I couldn't go into cpanel to have a look at it.