Network file sharing

Guys,
I´m desperate to death for help!

One of my clients has a Windows 2003 network, and an art depth with MACs. Since the MAC OS was updated, a problem started to happen. When a file of any kind, like font or pictures is accessed directly from the windows 2003 network sharing (located on the server), only a black figure appears and never the file itself.

Some MAC support guys told me that some versions of MAC OS 10 just doesn´t get it working. Is that true? Will I have to call the assistence to format them again?

Does anyone knows sometinhg about this problem? (If I copy locally the file, it doesn´t happens. Olnly when the file is directly opened from the server sharing).

If I don´t get this clue solved, I'm going to loose the contract.

Thaks in advance (sorry for my missing english).

Marcela.