Windows Server 2003 R2 NTFS 55 Error

We have a virtualized Windows Server 2003 R2.  It has been virtualized for almost 8 months now.  About two weeks ago we got an NTFS 55 Error stating "The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume \Device\HarddiskVolume1".  We rebooted the server it ran chkdsk there were no errors in the chkdsk summary.  The only thing that stood out in the chkdsk summary was that is re-allocated memory.  After that the server was running fine until 3 days later the same error.  We re-booted ran chkdsk and all was fine.  This error is now happening every 3 days exactly.  When the error occurs, services such as IIS and other critical services stop running.  Any ideas what could be causing this error to occur?  Nothing has changed on this server.  It runs a legacy system and is rarely touched.  I have attached screen shots of pre-chkdsk and post chkdsk.

Thanks,
Tim
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