I can't remember if one of the other lad's has posted this but here goes anyway:

Discreet Technical Support reports that 3ds max 5.1 has been certified to run on Microsoft Windows 2000 SP2 or Windows XP Pro SP1 only. Microsoft has recently released Service Pack 4 for Windows 2000. It is recommended that 3ds max not be run on this latest version. Issues may arise if later service packs are installed. Please avoid updating to service packs later than SP2 for Microsoft Windows 2000 or SP1 for Microsoft Windows XP.

We will post more information on this problem as it becomes available.

Issued by Discreet Product Support.

Discreet.com