Memcached Error 11 ERROR was returned by server received on get

Our PHP application has been running with Membase for several years connecting via the PHP Memcached Extension. We also have one instance of our application running on Couchbase 2.2.0. We have just installed a new server and we are testing our PHP application with Couchbase 2.5.0, PHP Memcached Extension 2.1.0, and libmemcache 1.0.18 on Ubuntu 12.04. These are newer versions than we have used in the past.

Some of our access that our PHP applications makes to Couchbase is working fine, however, when running thru our application test suite, we get an error the first time we try to retrieve from Couchbase a document via the Doctrine 1.2 result caching interface. The error received is MEMCACHED_ERROR, error code 11, Error was returned by server. I’ve pored over all the Couchbase logs but cannot find anything that tells me why the server returned an error. We are using igbinary serialization.

We have traced thru the code and the interface makes a call to the same address as the session caching calls which work. Is there some way to find out why Couchbase returns an error? and what the error is?

Any ideas what might be causing this? We’ve stared at it for days and haven’t been able to figure it out!