I found out the hard way that a Windows update for win2000 and XP causes Max files to be corrupted, so they are no longer usable. I wound up losing about a week's worth of work. I thought I would share this, and hopefully prevent someone else from suffering like I have.
From Discreet support:
Attention All 3ds max® and Autodesk® VIZ Customers,
SUBJECT: ALERT- 3ds max and Autodesk VIZ (.max) file corruption caused by recent Microsoft Windows Updates.
IMPACT:
Discreet has confirmed that Hotfix 823980 - contained in the Windows 2000 Service Pack 4 - causes the corruption of 3ds max and Autodesk VIZ (.max) files.
As a result, all .max files saved with Windows 2000 SP4 installed will no longer load in 3ds max or Autodesk VIZ on systems with Windows 2000 SP2, SP3 or SP4 installed.
We have also verified that this same Microsoft Windows Update Hotfix 823980 is also causing the same .max file corruption on XP operating systems. (Hotfix 823980 has been made available through Windows Update to all Windows 2000 and XP operating systems and service packs.)
WHO IS AFFECTED:
The following operating systems configurations will experience 3ds max and Autodesk VIZ file corruption:
Win 2K SP4
Hotfix KB 823980 under XP
Hotfix KB 823980 under Win2K SP3 or lower
Hotfix KB 823980 under Win NT 4
RESOLUTION:
Resolution of this problem and production work-arounds vary depending on a user's particular configuration, from the above list. Please follow the instructions below carefully to minimize any impact from this Windows Update defect.
Note that we are anticipating a new Hotfix fix from Microsoft by the end of July 2003 to resolve this problem. The temporary instructions below will allow affected systems to return to normal operation until this new Hotfix becomes publicly available.
In all cases, you should disable automatic windows updates through WinUpdate to avoid picking up Hotfix 823980 until the new Hotfix becomes available.
Temporary Instructions for Windows Update Hotfix 823980 Configurations
If the Windows Update Hotfix 823980 has already been installed under any Windows operating system, it is suggested that customers uninstall the Hotfix to create usable (.max) file content. Uninstalling Hotfix 823980 will allow existing or recently saved/corrupted files to be read by 3ds max and Autodesk VIZ without errors.
You can verify that the Hotfix is installed, and uninstall it, through the Control Panel >> Add/Remove Programs, then scroll to find the Windows Update referencing 823980. If it is installed, highlight the reference, and click remove to uninstall the fix.
WARNING - be sure to back-up any critical data on your system before uninstalling Hotfix 823980 or Windows 2K SP4.
Temporary Instructions for Windows 2K SP4 Configurations
Potential workaround for retrieval of files created or saved under Win 2K SP4:
Option 1, for Win 2K SP4 users:
(Please be aware that some 3ds max and Autodesk VIZ data will still be lost in this workaround.)
Revert Windows 2000 SP 4 Systems back to SP3 or earlier
Use "File Merge" to retrieve data from corrupted .maxfiles created under Windows 2000 SP4, and resave.
Note 1: If you have Render Effects or Atmospherics in your .maxfile, use the
Merge button in the respective dialogs.
Note 2: For Option 1, We recommend retaining any originally corrupted .max files until Microsoft resolves this issue through a future Hotfix.
Option 2, if Win XP OS is available:
Open corrupted .max files created under Windows 2000 SP4 in Windows XP without Hotfix 823980 installed, and resave.
Revert all systems back to Windows 2000 SP3 or previous and files should be corrected.
WARNING - be sure to back-up any critical data on your system before uninstalling Hotfix 823980 or Windows 2K SP4.
A man only needs one rectum. - F. Salter, "Recon Scout"
Forums 
