This Stop message, also known as Stop 0x50, occurs when requested data is not found in memory. The system generates a fault, which normally indicates that the system looks for data in the paging file. In this circumstance, however, the missing data is identified as being located within an area of memory that cannot be read to disk. The system faults, but cannot find, the data and is unable to recover. Faulty hardware, a buggy system service, antivirus software, and a corrupted NTFS volume can all generate this type of error.
Edit to add link: http://support.microsoft.com/?kbid=183169&sd=RMVP