ES 5.0.1, IO Adapter polling but not finding files

We are running ES 5.0.1 on Solaris. On two occassions now we have experienced a situation where the IO Adapter (version 4.0) is polling a directory but will not pick up files that are in the directory. It has lasted as long as 3 days, but goes away on it’s own and starts polling properly. Any clues?