Ok... I found the solution myself.
ESU could mount the volumes (the day I tried, the DNS-343 was probably busy doing something and did not allow it!).
After that, I found another problem: I was not able copying any file to the volumes on the NAS!!!
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Ok.... I started looking on internet for problems related to connecting Windows to Linux based devices.
After 1 hour of searching, I found this page on the internet... and I followed their suggestion.
The page is this: www.sevenforums.com/.../3737-samba-network-share-issue-windows-7-a.html
EVERYTHING FINE NOW!!!
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Hope this helps somebody else with my problem too!
