Can't save large files to NAS, but can save small ones

Question

I have the strangest problem;

We have a linux based NAS (QNAP 470). The is plenty of free diskspace (2TB out of 5TB) and everyone (+:- 50 people) is able to write to the NAS without problem, except 2 users who are using a Windows 7 machine.

Now comes the strangest part, they are able to read any file they have access to, but they are only able to modify or create small files (smaller than 8K). When they try to change/save/copy a file that is larger, they get an error stating they don't have permissions to do so.

You'll need to provide administrator permission to copy this folder

or

You need permission to perform this action. 
You'll need permission of the computer's administrator to make changes to this folder.

Permissions of these users are the same as those of other users. One of the two users recently had a reïnstall of her computer. Before the reinstall, she did not have this problem, so it must have got something to do with the windows installation. The Windows eventlog of these users does not log anything, nor the logfiles on the NAS.

Has anyone experienced a similar problem?

Answer 1

Thanks for thinking along, but I managed to find the problem, or at least the solution.

The NAS is Linux based and does not support the higher security Windows demands, as the computers are part of a Windows domain. I had to change following registry key and reboot in order to get the clients up and running.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\LanmanWorkstation\Parameters\RequireSecuritySignature

This is by default 1, but must be changed to 0 for them to be able to connect to the NAS.