I going to do a little guessing here, but I think that bit you've added at the end ought to be :./ not :.
With the ./, you're adding your current directory to your classpath and I think that is why you're getting the error message. Just a . doesn't quite do it. And the : is just the approved separator between the individual paths on the classpath.
That said, I run into this problem as well from time to time. The only reliable solution I've found is using the -classpath flag when I compile and run
javac -classpath ./:/any/other/driectory/I/need Filename.class