Exchange Server Error Code Look-up
Microsoft released an updated version (v6.0.4011.0) of the Exchange Server Error Code Look-up.
Overview
Use the Error Code Lookup tool to determine error values from decimal and hexadecimal error codes in Microsoft Windows® operating systems. The tool can look up one or more values at a time. All values on the command line will be looked up in Exchange’s internal tables and presented to you. If available, informational data associated with the value or values will also be shown.
Here are a couple of examples of the output of the tool:
C:\temp\Err>err 0x8004010f
# for hex 0x8004010f / decimal -2147221233 :
ecNotFound ec.h
ecAttachNotFound ec.h
ecUnknownRecip ec.h
ecPropNotExistent ec.h
MAPI_E_NOT_FOUND mapicode.h
# 5 matches found for "0x8004010f"
C:\temp\Err>Err.exe -528
# for decimal -528 / hex 0xfffffdf0 :
JET_errMissingLogFile esent98.h
# /* Current log file missing */
# 1 matches found for "-528"
TechRepublic has a great article about this: Quickly identify problems using the Exchange Error Code Look-up tool.