exchange 2010, Active directory

Did this event just start happening? How many DC do you have in the site where Exchange is hosted? Basically it is stating that it cannot keep up to the queries that users are requesting. I would check to see what your DC are doing and make sure that they have available resources as well (CPU and memory). You should also check and make sure the you network latency is also good.

Checking DC replication also wouldn't hurt. Probably not a good idea to just let this go. Are your clients complaining?

Will.

this error was generated 3 hrs back and is from exchange relay server

how do I check network latency

A simple ping can show the network latency. You can also use pathping as well.

I personally think it is to do with the resources on the DC's

Will.

what should be ldap normal search time

as I did tracert to google.com , all hops show less than 30 ms

what should be ldap normal search time , all dc are in site

if tracert  is less than 25ms , what should be the ldap search time?

you get 25ms on the same LAN? That seems high.

Or is this over a MPLS or IPSec VPN?

What about the resources on the DC's?

Will.

tracert to google  took less than 10ms

Just saw you accepted my solution.

Glad to have been able to help you so quickly.

When I was an Exchange Escalation engineer for MS this was the first thing we did when seeing high LDAP times.