Evidently if my CAESAR II file is named with periods in the file name - e.g. if I wanted to use today's date as 06.17.2015, CAESAR will drop off the .2015, and pop up an error message, saying that CAESAR can't find 06.17._A.

Exact phrasing of the help is as follows, to assist others in finding this should they run into the same issue:

ERROR: file
"[directory\truncated filename.A]" not found! Make sure you indeed created it.