Windows 2000 ‘suspends’ mapped drives ?

In our environment, we have windows 2000 clients mapping drives on NT servers. Any mapped drive that is not used for a period of time is suspended (my term) by windows. They appear with a red ‘X’ in “MY Computer”. While they reconnect immeadiately when clicked on, this seems to be causing a problem for certain software, such as Lotus notes. Can anyone shed some light on how this works and how it might be controled?