Can't access dropbox site

From about two days, I can't access https://www.dropbox.com from only one machine (Windows server 2003 R2 machine) while from all other clients in the same Windows domain I can access the same site without issue.

I've repeated the access via Chrome and I.e. 8 with the same result:

Chrome:

I.e. 8

I haven't no firewall that block any IP, protocol, etc...

Any idea