Fixing the JRE compatibility issue
A project created in a new version of Eclipse/JRE may not run properly when loaded in Eclipse on another computer with an older version of the JRE.
Follow these steps to hopefully fix this problem. You can do it at any point in the dev process.
Open Eclipse, verify your project is loaded in the Project Explorer
Right-click on the project in Project Explorer
Select Build Path
Select Configure Build Path
Click on Libraries Tab
If there is a system library, remove it
Click on the Add Library Button
Select JRE System Library
Click Next
Under System Library: Select "Execution Environment"
Click Finish
Click Apply and Close