Could not find or load main class

Question

I have Windows 7, installed jdk1.7.0 and its supporting jre7.
My problem is compilation part works perfectly, but while running the Java program I get this error saying:

Answer 1

I had almost the same problem, but with the following variation:

1. I've imported a ready-to-use maven project into Eclipse IDE from PC1 (project was working there perfectly) to another PC2
2. when was trying to run the project on PC 2 got the same error "Could not find or load main class"
3. I've checked PATH variable (it had many values in my case) and added JAVA_HOME variable (in my case it was JAVA_HOME = C:\Program Files\Java\jdk1.7.0_03) After restarting Ecplise it still didn't work
4. I've tried to run simple HelloWorld.java on PC2 (in another project) - it worked
5. So I've added HelloWorld class to the imported recently project, executed it there and - huh - my main class in that project started to run normally also.

That's quite odd behavour, I cannot completely understand it. Hope It'll help somebody. too.