In my case, this error is to be expected because my node is not using the default port of 3000. When I specify the proper port number (3020, in this case), all is well:
[dm@localhost ~]$ aql -p 3020
Aerospike Query
Copyright 2013 Aerospike. All rights reserved.
aql> show bins
0 rows in set (0.001 secs)
0 rows in set (0.000 secs)
OK
aql> show sets
0 rows in set (0.000 secs)
0 rows in set (0.000 secs)
OK
(yes, I know that I have no bins and no sets. This is in a test environment, and it is intentional.)