Eclipse: false error with jdk7

Question

I've been having a problem with eclipse that's been stressing me a lot. Whenever I start a new Java porject, everything goes smoothly and perfect, until I "clean" the project (Project -> Clean...) and everything goes to @#~%&...
I keep getting:

• XYZ cannot be resolved to a type
• Multi-catch parameters are not allowed for source level below 1.7
• <> operator is not allowed for source level below 1.7

That's very nice, only that I am importing all required classes and I do have 1.7 since the begginig. It's the only version I've installed. I've already tried this and other similar responses for the last few days with no avail.
A solution was to create a new project, copy and paste all packages/clases, which worked for a while, but I added UMLet to the project and again... Removing UMLet plugin did nothing for me.

BTW, even with the "errors", my project runs without any problem, therefore I know they're not real. I could keep working, but then, I can't see when a real error arises... Does anyone got a final solution to get rid of this false errors?

EDIT: I forgot to mention that I'm working with Kepler.

EDIT 2:

Here are screen captures with the requested information.

Answer 1

You can solve this by setting up correct JRE environment in Eclipse as below.

1. Go to Project => Properties => Java Build Path
2. Click on Libraries
3. Select JRE System Library
4. Click on Edit button at right hand side
5. Set Execution Environment to Jave SE-1.7(jre7)
6. Clean project or refresh project.