Event ID - 2103

Event Id2103
DescriptionProcess %1 (PID=%2). All Global Catalog Servers in use are not responding:
Event InformationExplanation :
This event indicates that DSAccess was not able to find any Global Catalogs suitable for LDAP queries. This can result in the halting of mail flow and interruption of Address Book services, so it should be investigated immediately. 
Causes can include all intra- and extra-site Global Catalogs being down or network problems hindering communication with them. 

User Action :
One possibility is that DSAccess could not find any suitable Global Catalogs when it did its initial topology discovery (whenever DSAccess starts, such as at Exchange server boot-up).
In this case, check the event log for DSAccess event ID 2080 (may need to increase the DSAccess logging level to record this event). The detail in that event will allow one to determine if GCs have been contacted that are unsuitable for some reason. They can then be corrected. 

Another possibility is that GCs already in use have become unsuitable (for example, by having lost contact due to network problems, LDAP port problems, etc.). Look for DSAccess event ID 2070 in the event logs. These events will detail why each GC has become unsuitable. Correct as necessary.
Reference Links Exchange System Attendant Does Not Start and You Receive a "Global Catalog Servers Not Responding" Error Message

Event ID 2080 from MSExchangeDSAccess

Policytest Utility Returns Right NOT Found Result

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