Welcome to "Alphabetically Challenged"!
This film-canister, guard-rail cache IS at the posted coordinates. However, this is a challenge cache, which means that, while you can sign the log at any time, you cannot log a "Found It" until you've also completed the challenge.
The challenge: On one single calendar day, find 26 caches, with one cache title for each letter of the alphabet. The title of the cache must START with the target letter. For example, if on that single day you've found caches entitled "Ant Attack", "Bug Invaders" and "Cockroach Haven", you've got A, B and C covered, but you'd still need to find the caches to represent D through Z. You do NOT need to find them in alphabetical order, but you DO need to find them all on the same day.
When you log your Found It, make sure to list the names and GC numbers of each of the caches in your log (or create a bookmark list) so it can be easily verified that you did indeed complete the challenge. Found It logs for cachers that have not yet completed the challenge will be deleted.
Good luck...and Cache On!