Topic Last Modified: 2007-02-19

The Microsoft Exchange Database Troubleshooter Tool detected one or more MSExchangeIS 9519 events with error code 0xfffff05b in the Application log. This error indicates that the Exchange database or transaction log files are located on a drive that has file system compression enabled.


This event may occur when you apply Exchange 2000 Server Service Pack 3 (SP3) to an Exchange 2000 Server that contains an information store database that is compressed by using NTFS file system compression. This issue may also occur when you upgrade an Exchange 2000 Server computer to Exchange Server 2003. Exchange 2000 Server SP3, Exchange Server 2003, and Exchange Server 2007 prevent compressed information store databases from mounting.

This error can also be identified as -4005, JET_errFileCompressed. This error applies to the following versions of Exchange server:

  • Microsoft Exchange Server 2007

  • Microsoft Exchange Server 2003

  • Microsoft Exchange 2000 Server SP3

User Action

To resolve this issue, you must decompress the folders where the information store databases and logs reside, defragment the databases, and then perform an online Exchange-aware backup of the Information Store storage groups where the databases and logs reside. To do this, see Microsoft Knowledge Base article 327772, Database does not mount, and you receive error 0xfffff05b after you apply SP3 to Exchange 2000.