Random Java errors that don't make sense

[TubaMorg]

Netbeans automatic error detection can get confused sometimes. Often closing a project and Netbeans, then reopening it will help. But it sounds as if you've already done it. You say it compiles fine? But it still shows errors? Another thing to check is to make sure the project library paths and Java version are set correctly. Sometimes updates will mess those up.
Also try "clean and build". You said you reinstalled Netbeans, did you redo the update too?

Another thing to do that might work is to start a new FIRST project and move your old files to the new project and rebuild.