Without message “Sharing Violation”

I have a Windows 2000 Server with many shared folders in my network. In each folder i have .exe files for my users.
When users access the files with Win98 and i try change de exe files i receive the message “Sharing Violation”. It’s normal.
When users access the files with Win2000 Prof or/and Win XP i cant change/delete the files whitout any kind of messages.
Why this happen?