Ambiguous registry access permission to delete value

[AndyHancock]

I am using windows XP and doing damage control for malware (http://
www.spywareremove.com/removeAntivirusSuite.html). In step 2, one of
the registry values that I have to delete (among others) is:

reg delete 'HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows
\CurrentVersion\Run' /v flnlxxjd /f

All the other registry value deletions were successful (with the
exception of two that didn't exist), but the above generated the error
"Access is denied". However I was able to delete that value using
regedit.

Why would I be denied access via the reg command, but not via regedit?