expire_fragment with memcached

I'm using the timed fragment caching plugin (
http://github.com/georgepalmer/timed_fragment_cache/tree/master )
with memcached and i have no problems.

Have you configured your caching storage as memcached?

Well, you could try to use the one i'm using, also, you shoudn't need
to "delete" things from memcached, it does it by itself when it
reaches it's memory limit.