During startup of Exchange the Microsoft Exchange Services do not start. This error can occur if a domain controller or GC (Global Catalog) is not available during startup or has a very slow link. 

The following error is logged in the eventviewer:

Event ID: 1005
Event Source: MSExchangeSA
Unexpected error An unknown error has occurred. ID no: 80040a01 Microsoft Exchange System Attendant occurred.

Exchange needs to contact a GC during startup for topology creation. There is a default timeout since Exchange 2000 SP2 of 1 minute. If no domain controller can be contacted in that length of time the System Attendant generates error 0×80040a01 (DSAccess topology creation timeout).

This behaviour can also occur on Domain Controllers where Exchange is installed, although this is not a recommended installation. The error applies to Exchange 2000 SP2 or higher (thus also Exchange 2003).

Solution

Create a new value in the following key on the Exchange Server:

HKEY_LOCAL_Machine\System\CurrentControlSet\Services\MSExchangeDSAccess

Value: TopoCreateTimeoutSecs (DWORD)
Data: 600 (decimal)

The data represents the number of seconds for the timeout. In this example 600 seconds, equals 10 minutes.

For more info :
XADM: Exchange 2000 Services Do Not Start and a “0×80040a01″ Error Message Is Logged