Error on standby: Cannot assign TransactionIDs during recovery.

I get this error on the standby node when using check_postgres.pl for the
following actions:

Autovacuum_freeze

Txn_wraparound.

I tried running the following query on the standby:

SELECT datname, age(datfrozenxid) AS age FROM pg_database WHERE
datallowconn ORDER BY 1, 2;

The resulting error is as follows:
ERROR: cannot assign TransactionIds during recovery

Posgres version: 9.0.7

Thanks!
Anit