Windows 7: "access denied" when using "assoc" and "ftype" from cmdline?

I tried to associate the file extension .txt to a new editor program
with the well known cmdline programs ASSOC and FTYPE.

No, assigning them through WinExplorer menu does not work.
But this is another problem which should not discussed here.

When I type now one of the following alternative commands at the CommandPrompt then Windows 7 returns me something like:

assoc .txt=txtfile

"Access denied"
The following error occurs: .txt"

or

ftype txtfile=D:\notepad++\notepad++.exe "%%1"

"Access denied"
The following error occurs: txtfile"

Why?

The command above work fine under WinXP

Peter

Question:

Did you run cmd.exe with administrative previlliges?
Elevated Command Prompt