Redis not allowing any operations
===

I have a Redis server. 
When I try the ping command or any other command using
redis-cli ping
I get an error message saying :
(error) ERR operation not permitted

typing only redis-cli takes me to the prompt :
redis 127.0.0.1:6379>

after this any redis command again gives the same error.

I have no idea what the issue could be.
Any help is appreciated.